JP2017068884A - Magnetic recording medium, magnetic signal reproduction device, and manufacturing method of magnetic recording medium - Google Patents
Magnetic recording medium, magnetic signal reproduction device, and manufacturing method of magnetic recording medium Download PDFInfo
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- JP2017068884A JP2017068884A JP2015195161A JP2015195161A JP2017068884A JP 2017068884 A JP2017068884 A JP 2017068884A JP 2015195161 A JP2015195161 A JP 2015195161A JP 2015195161 A JP2015195161 A JP 2015195161A JP 2017068884 A JP2017068884 A JP 2017068884A
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- recording medium
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Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/62—Record carriers characterised by the selection of the material
- G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
- G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
- G11B5/708—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by addition of non-magnetic particles to the layer
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/62—Record carriers characterised by the selection of the material
- G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/62—Record carriers characterised by the selection of the material
- G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
- G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/62—Record carriers characterised by the selection of the material
- G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
- G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
- G11B5/708—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by addition of non-magnetic particles to the layer
- G11B5/7085—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by addition of non-magnetic particles to the layer non-magnetic abrasive particles
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/62—Record carriers characterised by the selection of the material
- G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
- G11B5/735—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer characterised by the back layer
Abstract
Description
本発明は、磁気記録媒体、磁気信号再生装置、および磁気記録媒体の製造方法に関する。 The present invention relates to a magnetic recording medium, a magnetic signal reproducing apparatus, and a method for manufacturing a magnetic recording medium.
塗布型磁気記録媒体は、非磁性支持体上に強磁性粉末および結合剤を含む磁性層を有し、任意に、非磁性支持体と磁性層との間に、非磁性粉末および結合剤を含む非磁性層を有する。 The coated magnetic recording medium has a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support, and optionally contains a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer. It has a nonmagnetic layer.
従来、塗布型磁気記録媒体の磁性層に、強磁性粉末とともに、走行時の摩擦係数の低減に寄与する非磁性粉末（非磁性粒子）を含有させることが行われてきた（例えば特許文献１参照）。 Conventionally, a magnetic layer of a coating-type magnetic recording medium has been made to contain a nonmagnetic powder (nonmagnetic particles) that contributes to a reduction in the friction coefficient during running together with a ferromagnetic powder (see, for example, Patent Document 1). ).
磁気記録媒体に記録された信号を、磁気記録媒体表面（磁性層側表面）と磁気ヘッドとを接触（摺動）させながら再生する際（走行時）、摩擦係数が高いと、走行安定性の低下によるノイズ増大や、磁気記録媒体表面の削れにより発生した異物が磁気ヘッドに付着することによる出力変動（スペーシングロス）の原因となる。このような現象の発生を抑制するためには、摩擦係数を低減することが望ましく、そのために、上記の非磁性粒子を磁性層に含有させることは有効である。走行時の摩擦係数の増大は、磁気記録媒体表面と磁気ヘッドとが接触する際の接触面積（いわゆる真実接触面積）を低減することにより抑えることができ、上記の非磁性粒子は、磁気記録媒体表面に適度な粗さを付与することにより真実接触面積の低減に寄与すると考えられるためである。
しかし他方で、磁気記録媒体表面が粗くなると、信号再生時の磁気ヘッド／磁気記録媒体表面間のスペーシングの増大による出力低下が発生し、電磁変換特性（ＳＮＲ；Signal-to-Noise ratio）は低下してしまう。即ち、走行時の摩擦係数の低減と電磁変換特性の向上は、トレードオフの関係にあり、両立することは容易ではない。
この点に関し、特許文献１には、摩擦係数の低減（特許文献１には、摩擦特性の向上と記載されている。）と電磁変換特性とを両立するための手段が提案されている。しかしながら、本発明者の検討によれば、走行時の摩擦係数の低減を達成しながら、電磁変換特性をより一層向上するためには、特許文献１に記載の磁気記録媒体には、更なる改善が望まれる。
When the signal recorded on the magnetic recording medium is reproduced while the magnetic recording medium surface (magnetic layer side surface) and the magnetic head are in contact (sliding) (during running), a high friction coefficient can improve running stability. This causes noise increase due to the decrease, and output fluctuation (spacing loss) due to foreign matter generated by the scraping of the magnetic recording medium surface adhering to the magnetic head. In order to suppress the occurrence of such a phenomenon, it is desirable to reduce the friction coefficient. For this purpose, it is effective to contain the above-mentioned nonmagnetic particles in the magnetic layer. The increase in the coefficient of friction during running can be suppressed by reducing the contact area (so-called true contact area) when the surface of the magnetic recording medium and the magnetic head are in contact with each other. It is because it is thought that it contributes to reduction of a true contact area by giving moderate roughness to the surface.
On the other hand, however, when the surface of the magnetic recording medium becomes rough, the output decreases due to an increase in spacing between the magnetic head and the surface of the magnetic recording medium at the time of signal reproduction, and the electromagnetic conversion characteristic (SNR: Signal-to-Noise ratio) is It will decline. That is, there is a trade-off between reducing the friction coefficient during running and improving the electromagnetic conversion characteristics, and it is not easy to achieve both.
In this regard, Patent Document 1 proposes means for achieving both reduction of the friction coefficient (described in Patent Document 1 as improvement of friction characteristics) and electromagnetic conversion characteristics. However, according to the study of the present inventors, in order to further improve the electromagnetic conversion characteristics while achieving a reduction in the friction coefficient during running, the magnetic recording medium described in Patent Document 1 is further improved. Is desired.
本発明の目的は、走行時の摩擦係数の低減と電磁変換特性のより一層の向上を達成することができる磁気記録媒体を提供することにある。 An object of the present invention is to provide a magnetic recording medium that can achieve a reduction in a coefficient of friction during traveling and a further improvement in electromagnetic conversion characteristics.
本発明者は、上記目的を達成するために鋭意検討を重ねた結果、以下の磁気記録媒体：
非磁性支持体上に強磁性粉末および結合剤を含む磁性層を有する磁気記録媒体であって、
磁性層は、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である複数個の非磁性粒子を含み、
上記複数個の非磁性粒子は、走査型電子顕微鏡により撮像される断面画像において観察される各非磁性粒子の磁性層埋没深さをｂ、磁性層の厚みをｔとして、比率ｂ／ｔの平均値が０．９以下の状態で上記磁性層に存在し、
磁気記録媒体の磁性層側の表面において原子間力顕微鏡により測定される突起の個数は、面積４０μｍ×４０μｍあたり、高さ５ｎｍ以上の突起の個数が８００個以上であり、かつ高さ２０ｎｍ以上の突起の個数が２０個以下である磁気記録媒体、
を見出すに至った。
As a result of intensive studies to achieve the above object, the present inventor has obtained the following magnetic recording medium:
A magnetic recording medium having a magnetic layer comprising a ferromagnetic powder and a binder on a nonmagnetic support,
The magnetic layer includes a plurality of nonmagnetic particles having a major axis length / minor axis length ratio (major axis length / minor axis length) of 1.5 or less,
The plurality of nonmagnetic particles have an average ratio b / t, where b is the buried depth of the magnetic layer of each nonmagnetic particle observed in a cross-sectional image captured by a scanning electron microscope, and t is the thickness of the magnetic layer. Present in the magnetic layer with a value of 0.9 or less,
The number of protrusions measured by an atomic force microscope on the surface of the magnetic recording medium side of the magnetic recording medium is 800 or more protrusions having a height of 5 nm or more per area of 40 μm × 40 μm and 20 nm or more in height. A magnetic recording medium having 20 or less protrusions;
I came to find.
上記磁気記録媒体によれば、走行時の摩擦係数を低減することができ、かつ特許文献１に記載の磁気記録媒体により実現される電磁変換特性より更に優れた電磁変換特性を得ることができる。以下は、本発明を何ら限定するものではないが、この点について、本発明者は、次のように考えている。 According to the above magnetic recording medium, it is possible to reduce the friction coefficient during running and to obtain electromagnetic conversion characteristics that are even better than the electromagnetic conversion characteristics realized by the magnetic recording medium described in Patent Document 1. The following is not intended to limit the present invention, but the present inventor considers this point as follows.
（１）長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である複数個の非磁性粒子が、走査型電子顕微鏡により撮像される断面画像において観察される各非磁性粒子の磁性層埋没深さ（以下、「埋没深さ」とも記載する。）をｂ、磁性層の厚みをｔとして、比率ｂ／ｔの平均値が０．９以下の状態で磁性層に存在することが、電磁変換特性の更なる向上に寄与すると、本発明者は推察している。詳しくは、以下の通りである。
本発明者は、特許文献１に記載の磁気記録媒体において電磁変換特性の更なる向上を妨げる要因は、走行時の摩擦係数低減のために磁性層に含有させた非磁性粒子が、磁性層の厚み方向全域を占めてしまうからではないかと考えた。上記非磁性粒子は、特許文献１に記載の磁気記録媒体では、磁性層の厚みを１とすると、１．１倍以上（詳しくは１．１倍以上８．０倍以下）の平均粒径を有するため（特許文献１の請求項１参照）、厚み方向全域を占めてしまう可能性が高いと考えられる。なお上記非磁性粒子が磁性層の厚み方向全域を占めると、上記の埋没深さｂの磁性層の厚みに対する比率ｂ／ｔは１．０となる。
これに対し、上記磁気記録媒体は、上記の埋没深さｂの磁性層の厚みに対する比率ｂ／ｔの平均値が０．９以下である。これは、上記非磁性粒子の多くが、磁性層の厚み方向全域を占めずに、磁性層において、磁性層と隣接する非磁性支持体または詳細を後述する非磁性層との界面近傍に上記非磁性粒子に占められていない領域があることを意味する。この状態で上記非磁性粒子が存在することが、電磁変換特性の更なる向上に寄与すると、本発明者は考えている。
なお上記非磁性粒子として、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である非磁性粒子を規定する理由は、磁気記録媒体表面に突出し適度な粗さを付与することにより真実接触面積の低減に寄与し得る非磁性粒子を規定するためである。
(1) A plurality of nonmagnetic particles having a major axis length / minor axis length ratio (major axis length / minor axis length) of 1.5 or less are observed in a cross-sectional image captured by a scanning electron microscope. In the state where the average value of the ratio b / t is 0.9 or less, where b is the buried depth of the magnetic layer of each nonmagnetic particle (hereinafter also referred to as “embedded depth”) and t is the thickness of the magnetic layer. The present inventor has inferred that the presence in the magnetic layer contributes to further improvement in electromagnetic conversion characteristics. Details are as follows.
The present inventor has found that the non-magnetic particles contained in the magnetic layer in order to reduce the friction coefficient during running are the factors that hinder the further improvement of the electromagnetic conversion characteristics in the magnetic recording medium described in Patent Document 1. I thought that it might occupy the whole area in the thickness direction. In the magnetic recording medium described in Patent Document 1, the nonmagnetic particles have an average particle diameter of 1.1 times or more (specifically, 1.1 times or more and 8.0 times or less) when the thickness of the magnetic layer is 1. Therefore, the possibility of occupying the entire region in the thickness direction is considered high. When the nonmagnetic particles occupy the entire thickness direction of the magnetic layer, the ratio b / t of the buried depth b to the thickness of the magnetic layer is 1.0.
In contrast, in the magnetic recording medium, the average value of the ratio b / t of the buried depth b to the thickness of the magnetic layer is 0.9 or less. This is because most of the non-magnetic particles do not occupy the entire thickness direction of the magnetic layer, and in the magnetic layer, the non-magnetic support is adjacent to the magnetic layer or the interface between the non-magnetic layer, which will be described in detail later, is not It means that there is a region not occupied by magnetic particles. The present inventor believes that the presence of the non-magnetic particles in this state contributes to further improvement of electromagnetic conversion characteristics.
The reason why the ratio of the major axis length to the minor axis length (major axis length / minor axis length) is 1.5 or less is defined as the nonmagnetic particle because it protrudes from the surface of the magnetic recording medium. This is to define non-magnetic particles that can contribute to the reduction of the true contact area by imparting roughness.
（２）磁気記録媒体の磁性層側の表面において原子間力顕微鏡により測定される突起の個数が、面積４０μｍ×４０μｍあたり、高さ５ｎｍ以上の突起の個数が８００個以上であり、かつ高さ２０ｎｍ以上の突起の個数が２０個以下であることが、電磁変換特性の更なる向上を妨げることなく、走行時の摩擦係数を低減することに寄与すると、本発明者は推察している。詳しくは、電磁変換特性の更なる向上を妨げると考えられる高さ２０ｎｍ以上の突起の個数は低減し、かつ電磁変換特性の更なる向上を妨げずに走行時に磁気記録媒体表面と磁気ヘッドとが接触する際の真実接触面積の低減に寄与すると考えられる高さ５ｎｍの突起を適度に存在させることが、電磁変換特性の更なる向上を妨げることなく、走行時の摩擦係数を低減することに寄与すると、本発明者は考えている。 (2) The number of protrusions measured by an atomic force microscope on the surface of the magnetic recording medium side of the magnetic recording medium is 800 or more protrusions having a height of 5 nm or more per area of 40 μm × 40 μm, and the height The present inventor has inferred that the number of protrusions of 20 nm or more being 20 or less contributes to reducing the friction coefficient during traveling without hindering further improvement in electromagnetic conversion characteristics. Specifically, the number of protrusions having a height of 20 nm or more, which is considered to hinder further improvement of the electromagnetic conversion characteristics, is reduced, and the surface of the magnetic recording medium and the magnetic head are moved during running without hindering further improvement of the electromagnetic conversion characteristics. Appropriate presence of protrusions with a height of 5 nm, which is thought to contribute to the reduction of the true contact area when contacting, contributes to reducing the friction coefficient during travel without hindering further improvement in electromagnetic conversion characteristics. Then, this inventor thinks.
ただし以上は推察に過ぎず、本発明を何ら限定するものではない。 However, the above is only an estimation and does not limit the present invention.
一態様では、上記磁性層に含まれる長軸長と短軸長との比率（長軸長／短軸長）が１．５以下の複数個の非磁性粒子の平均長軸長φの磁性層の厚みｔに対する比率φ／ｔは、１．０以下である。 In one aspect, a magnetic layer having an average major axis length φ of a plurality of nonmagnetic particles having a major axis length / minor axis length ratio (major axis length / minor axis length) of 1.5 or less. The ratio φ / t to the thickness t is 1.0 or less.
一態様では、上記磁性層に含まれる長軸長と短軸長との比率（長軸長／短軸長）が１．５以下の複数個の非磁性粒子の平均長軸長φは、１０〜１００ｎｍの範囲である。 In one embodiment, the average major axis length φ of a plurality of nonmagnetic particles having a ratio of major axis length to minor axis length (major axis length / minor axis length) included in the magnetic layer of 1.5 or less is 10 It is in the range of ˜100 nm.
一態様では、上記磁性層の厚みｔは、１００ｎｍ以下である。 In one embodiment, the thickness t of the magnetic layer is 100 nm or less.
一態様では、上記磁性層に含まれる長軸長と短軸長との比率（長軸長／短軸長）が１．５以下の複数個の非磁性粒子は、無機酸化物粒子である。 In one embodiment, the plurality of nonmagnetic particles having a major axis length / minor axis length ratio (major axis length / minor axis length) included in the magnetic layer of 1.5 or less are inorganic oxide particles.
一態様では、上記無機酸化物粒子は、珪素酸化物粒子である。 In one aspect, the inorganic oxide particles are silicon oxide particles.
一態様では、上記珪素酸化物粒子は、シリカコロイド粒子である。 In one aspect, the silicon oxide particles are silica colloid particles.
一態様では、上記磁気記録媒体の磁性層側の表面において原子間力顕微鏡により測定される高さ５ｎｍ以上の突起の個数は、面積４０μｍ×４０μｍあたり、８００個以上５００，０００個以下である。 In one embodiment, the number of protrusions having a height of 5 nm or more measured by an atomic force microscope on the surface on the magnetic layer side of the magnetic recording medium is 800 or more and 500,000 or less per area of 40 μm × 40 μm.
一態様では、上記磁気記録媒体の磁性層側の表面において原子間力顕微鏡により測定される高さ５ｎｍ以上の突起の個数は、面積４０μｍ×４０μｍあたり、４０００個以上である。 In one embodiment, the number of protrusions having a height of 5 nm or more measured by an atomic force microscope on the surface of the magnetic recording medium on the magnetic layer side is 4000 or more per area of 40 μm × 40 μm.
一態様では、上記磁気記録媒体の磁性層側の表面において原子間力顕微鏡により測定される高さ２０ｎｍ以上の突起の個数は、面積４０μｍ×４０μｍあたり、１０個以下である。 In one embodiment, the number of protrusions having a height of 20 nm or more measured by an atomic force microscope on the surface on the magnetic layer side of the magnetic recording medium is 10 or less per 40 μm × 40 μm area.
一態様では、上記磁気記録媒体は、非磁性支持体と磁性層との間に、非磁性粉末および結合剤を含む非磁性層を有する。 In one aspect, the magnetic recording medium has a nonmagnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer.
本発明の更なる態様は、上記磁気記録媒体と、磁気再生ヘッドと、を含む磁気信号再生装置に関する A further aspect of the present invention relates to a magnetic signal reproducing apparatus including the magnetic recording medium and a magnetic reproducing head.
一態様では、上記磁気信号再生装置は、上記磁気記録媒体に２００ｋｆｃｉ以上の線記録密度で記録された磁気信号を、上記磁気再生ヘッドで再生する磁気信号再生装置である。 In one aspect, the magnetic signal reproducing device is a magnetic signal reproducing device that reproduces a magnetic signal recorded on the magnetic recording medium at a linear recording density of 200 kfci or more with the magnetic reproducing head.
本発明の更なる態様は、
上記磁気記録媒体の製造方法であって、
磁性層形成工程を含み、
上記磁性層形成工程は、
強磁性粉末および結合剤を含む磁性塗布膜形成用組成物、ただし、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である非磁性粒子を含まない、を非磁性支持体上に、直接または一層以上の他の層を介して塗布および乾燥することにより磁性塗布膜を形成すること、
上記磁性塗布膜上に、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である複数個の非磁性粒子および溶媒を含むオーバーコート液を塗布および乾燥することにより上記非磁性粒子を上記磁性塗布膜上に配置すること、
上記配置した非磁性粒子を上記磁性塗布膜側へ押し込むことにより、強磁性粉末および結合剤を含み、かつ上記非磁性粒子が上記状態で存在する上記磁性層を形成すること、
を含む、上記磁気記録媒体の製造方法、
に関する。なお本発明において、上記磁性塗布膜形成用組成物が、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である非磁性粒子を「含まない」とは、上記組成物を調製する際の成分として積極的に用いないことを意味し、意図せず混入することは許容するものとする。例えば、上記磁性塗布膜形成用組成物に含まれる強磁性粉末１００質量部に対し、０．０１質量部以下程度の量で混入することは許容されるものとする。
A further aspect of the invention provides:
A method for producing the magnetic recording medium, comprising:
Including a magnetic layer forming step,
The magnetic layer forming step includes
Composition for forming magnetic coating film containing ferromagnetic powder and binder, except for non-magnetic particles having a major axis length / minor axis length ratio (major axis length / minor axis length) of 1.5 or less Forming a magnetic coating film on the non-magnetic support directly or through one or more other layers and drying.
On the magnetic coating film, an overcoat liquid containing a plurality of nonmagnetic particles and a solvent having a major axis length / minor axis length ratio (major axis length / minor axis length) of 1.5 or less is applied and dried. By disposing the non-magnetic particles on the magnetic coating film,
Forming the magnetic layer containing ferromagnetic powder and a binder and having the nonmagnetic particles present in the state by pushing the arranged nonmagnetic particles toward the magnetic coating film;
A method of manufacturing the magnetic recording medium,
About. In the present invention, the composition for forming a magnetic coating film “does not contain” non-magnetic particles having a major axis length / minor axis length ratio (major axis length / minor axis length) of 1.5 or less. Means that it is not actively used as a component in the preparation of the composition, and it is allowed to be mixed unintentionally. For example, it is allowed to be mixed in an amount of about 0.01 parts by mass or less with respect to 100 parts by mass of the ferromagnetic powder contained in the magnetic coating film forming composition.
本発明の一態様によれば、走行時の摩擦係数が低く、かつ電磁変換特性のより一層の向上が可能な磁気記録媒体を提供することができる。
更に本発明の一態様によれば、上記磁気記録媒体を含む磁気信号再生装置、および上記磁気記録媒体の製造方法を提供することもできる。
According to one embodiment of the present invention, it is possible to provide a magnetic recording medium that has a low friction coefficient during travel and can further improve electromagnetic conversion characteristics.
Furthermore, according to one aspect of the present invention, a magnetic signal reproducing apparatus including the magnetic recording medium and a method for manufacturing the magnetic recording medium can be provided.
［磁気記録媒体］
本発明の一態様は、以下の磁気記録媒体に関する。
非磁性支持体上に強磁性粉末および結合剤を含む磁性層を有する磁気記録媒体であって、
磁性層は、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である複数個の非磁性粒子を含み、
上記複数個の非磁性粒子は、走査型電子顕微鏡により撮像される断面画像において観察される各非磁性粒子の磁性層埋没深さをｂ、磁性層の厚みをｔとして、比率ｂ／ｔの平均値が０．９以下の状態で上記磁性層に存在し、
磁気記録媒体の磁性層側の表面において原子間力顕微鏡により測定される突起の個数は、面積４０μｍ×４０μｍあたり、高さ５ｎｍ以上の突起の個数が８００個以上であり、かつ高さ２０ｎｍ以上の突起の個数が２０個以下である磁気記録媒体。
以下、上記磁気記録媒体について、更に詳細に説明する。
[Magnetic recording medium]
One aspect of the present invention relates to the following magnetic recording medium.
A magnetic recording medium having a magnetic layer comprising a ferromagnetic powder and a binder on a nonmagnetic support,
The magnetic layer includes a plurality of nonmagnetic particles having a major axis length / minor axis length ratio (major axis length / minor axis length) of 1.5 or less,
The plurality of nonmagnetic particles have an average ratio b / t, where b is the buried depth of the magnetic layer of each nonmagnetic particle observed in a cross-sectional image captured by a scanning electron microscope, and t is the thickness of the magnetic layer. Present in the magnetic layer with a value of 0.9 or less,
The number of protrusions measured by an atomic force microscope on the surface of the magnetic recording medium side of the magnetic recording medium is 800 or more protrusions having a height of 5 nm or more per area of 40 μm × 40 μm and 20 nm or more in height. A magnetic recording medium having 20 or less protrusions.
Hereinafter, the magnetic recording medium will be described in more detail.
なお本発明および本明細書において、非磁性粉末とは、複数個の非磁性粒子の集合を意味するものとする。集合とは、これを構成する粒子が直接接触している態様に限定されず、後述する結合剤や添加剤等が、粒子同士の間に介在している態様も包含される。なお粒子との語が、粉末を表すために用いられることもある。以上の点は、強磁性粉末等の、本発明および本明細書における各種粉末についても同様とする。 In the present invention and the present specification, the non-magnetic powder means an assembly of a plurality of non-magnetic particles. The term “aggregation” is not limited to the mode in which the particles constituting this are in direct contact, but also includes the mode in which binders, additives, and the like described later are interposed between the particles. The term “particle” is sometimes used to represent powder. The same applies to various powders in the present invention and the present specification, such as ferromagnetic powder.
＜比率ｂ／ｔの平均値＞
上記磁気記録媒体は、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である複数個の非磁性粒子を含み、これら複数個の非磁性粒子が、走査型電子顕微鏡（ＳＥＭ；Scanning Electron Microscope）により撮像される断面画像において観察される各非磁性粒子の埋没深さをｂ、磁性層の厚みをｔとして、比率ｂ／ｔの平均値が０．９以下の状態で磁性層に存在する。比率ｂ／ｔの平均値が０．９以下であることが、前述の特許文献１で実現された電磁変換特性より更に優れた電磁変換特性を達成することに寄与すると、本発明者は考えている。この点に関する本発明者の推察は、先に記載した通りである。更に一層優れた電磁変換特性を達成する観点からは、比率ｂ／ｔの平均値は、０．８以下であることが好ましく、０．７以下であることがより好ましく、０．６以下であることが更に好ましく、０．５以下であることが一層好ましい。比率ｂ／ｔの平均値は、例えば０．２以上または０．３以上であることができるが、電磁変換特性向上の観点からは、比率ｂ／ｔの平均値が小さいことは好ましいため、これらを下回ってもよい。
<Average value of ratio b / t>
The magnetic recording medium includes a plurality of nonmagnetic particles having a major axis length / minor axis length ratio (major axis length / minor axis length) of 1.5 or less. The average value of the ratio b / t is 0, where b is the buried depth of each nonmagnetic particle observed in a cross-sectional image taken by a scanning electron microscope (SEM), and t is the thickness of the magnetic layer. It exists in the magnetic layer in a state of 9 or less. The present inventor believes that the average value of the ratio b / t being 0.9 or less contributes to achieving electromagnetic conversion characteristics further superior to the electromagnetic conversion characteristics realized in Patent Document 1 described above. Yes. The inventor's inference regarding this point is as described above. From the viewpoint of achieving even more excellent electromagnetic conversion characteristics, the average value of the ratio b / t is preferably 0.8 or less, more preferably 0.7 or less, and 0.6 or less. More preferably, it is more preferably 0.5 or less. The average value of the ratio b / t can be, for example, 0.2 or more, or 0.3 or more. However, from the viewpoint of improving electromagnetic conversion characteristics, it is preferable that the average value of the ratio b / t is small. May be less than
（測定方法）
以上記載した比率ｂ／ｔの平均値は、以下の方法により求めるものとする。以下では、非磁性支持体上に非磁性層を有し、非磁性層上に磁性層を有する磁気記録媒体における測定を例に記載する。ただし、上記磁気記録媒体は、非磁性支持体上に直接磁性層を有する磁気記録媒体であってもよい。この場合、下記記載における界面とは、磁性層と非磁性支持体との界面となる。
（１）断面観察用試料の作製
断面観察用試料を、比率ｂ／ｔの平均値を求める対象の磁気記録媒体の無作為に定めた位置から切り出し作製する。断面観察用試料の作製は、ガリウムイオン（Ｇａ＋）ビームを用いるＦＩＢ（Focused Ion Beam；収束イオンビーム）加工によって行う。かかる作製方法の具体例は、実施例について後述する。
（２）観察領域の特定
作製した断面観察用試料をＳＥＭ観察し、断面画像（ＳＥＭ像）を撮像する。走査型電子顕微鏡としては、電界放射型走査型電子顕微鏡（ＦＥ(Field Emission)−ＳＥＭ）を用いる。例えば日立製作所製ＦＥ−ＳＥＭ Ｓ４８００を用いることができ、後述の実施例ではこのＦＥ−ＳＥＭを用いた。
ＳＥＭ像は、同一の断面観察用試料において、
（ｉ）撮像する範囲が重複しないように、
（ｉｉ）磁性層側表面（磁性層表面）および磁性層側表面に突出している非磁性粒子がＳＥＭ像に収まるように、かつ
（ｉｉｉ）断面観察用試料の磁性層の厚み方向全域（即ち、磁性層側表面から磁性層と非磁性層との界面までの領域）および磁性層と非磁性層との界面を貫いている非磁性粒子が存在する場合にはかかる非磁性粒子がＳＥＭ像に収まるように、
選択する点以外は無作為に選択した位置において撮像し、合計４画像得る。上記ＳＥＭ像は、加速電圧５ｋＶ、撮像倍率１０万倍および縦９６０画素（ｐｉｘｅｌ）×横１２８０画素で撮像される二次電子像（ＳＥ（secondary electron)像）である。
なおＳＥＭ像において、強磁性粉末と非磁性粉末（非磁性粒子）とは、画像上での濃淡の違い、サイズの違い、形状の違い等から、容易に区別することができる。非磁性粒子を構成する素材は、エネルギー分散型Ｘ線分光法（ＥＤＳ：Energy Dispersive X-ray Spectrometry）、オージェ電子分光法（ＡＥＳ：Auger Electron Spectroscopy）、走査型電子顕微鏡による磁性層表面における成分のマッピング等の組成分析可能な公知の方法により解析することもできる。
（３）磁性層の厚みｔの測定
撮像されたＳＥＭ像を、画像処理ソフト三谷商事株式会社製ＷｉｎＲＯＯＦに取り込み、ＳＥＭ像中の磁性層の部分（観察領域）を選択する。観察領域の選択において、観察領域の幅方向の長さは、撮像されたＳＥＭ像の全幅とする。なお、ＳＥＭ像に関して記載する幅方向とは、撮像された断面観察用試料における幅方向をいう。断面観察用試料における幅方向とは、この試料を切り出した磁気記録媒体における幅方向である。以上について、厚み方向についても、同様とする。
厚み方向に関して、磁性層と非磁性層との界面は、以下の方法により特定する。ＳＥＭ像をデジタル化して厚み方向の画像輝度データ（厚み方向の座標、幅方向の座標、および輝度の３成分からなる。）を作成する。デジタル化では、ＳＥＭ像を幅方向に１２８０分割して、輝度８ビットで処理して２５６階調のデータを得て、分割した各座標ポイントの画像輝度を所定の階調値に変換する。次に、得られた画像輝度データにおいて、厚み方向の各座標ポイントにおける幅方向の輝度の平均値（即ち、１２８０分割した各座標ポイントにおける輝度の平均値）を縦軸にとり、厚み方向の座標を横軸にとって輝度曲線を作成する。作成した輝度曲線を微分して微分曲線を作成し、作成した微分曲線のピーク位置から磁性層と非磁性層との境界の座標を特定する。ＳＥＭ像上の、特定した座標に相当する位置を、磁性層と非磁性層との界面とする。
磁性層側表面も、上記と同様に輝度曲線を用いて特定する。
撮像した４画像の各画像の任意の位置の１箇所で、特定した磁性層側表面と、磁性層と非磁性層との界面との直線最短距離を求め、４画像で求めた値の平均値を、磁性層の厚みｔとする。なお本発明および本明細書において、平均値とは、算術平均をいう。
（４）長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である非磁性粒子の特定
撮像した４画像の各画像中の非磁性粒子の部分を、画像輝度データから特定し、画像解析により長軸長および短軸長を求める。具体的には、各画像（ＳＥＭ像）をデジタル化して、非磁性粒子の長軸方向、短軸方向の画像輝度データ（長軸方向の座標、短軸方向の座標、および輝度の３成分からなる。）を作成する。デジタル化では、ＳＥＭ像を幅方向に１２８０分割して、輝度８ビットで処理して２５６階調のデータを得て、分割した各座標ポイントの画像輝度を所定の階調値に変換する。次に、得られた画像輝度データにおいて、粒子の長軸にあたる方向の座標を横軸にとり、長軸方向の各座標ポイントにおける輝度の平均値（即ち、１２８０分割した各座標ポイントにおける輝度の平均値）を縦軸にとって輝度曲線を作成する。作成した輝度曲線を微分して微分曲線を作成し、作成した微分曲線のピーク位置から非磁性粒子部分の境界の座標を特定する。粒子の長軸にあたる方向の座標を横軸にとる操作を３回繰り返し、最も長い軸長を長軸長とする。短軸方向でも座標を横軸にとる操作を３回繰り返し、最も短い軸長を短軸長とする。詳しくは、長軸長とは、粒子の長さを最も長く取ることができる軸（直線）を長軸として決定し、この長軸の長さとする。一方、短軸とは、長軸と直交する直線で粒子長さを取ったときに最も長さが長くなる軸として決定し、この軸の長さを短軸長とする。ただし、形状から粒子を構成する長軸および／または短軸を特定できない不定形の非磁性粒子は、測定対象外する。また、長軸長と短軸長との比率（長軸長／短軸長）が１．５を超えることが一見して明らかな非磁性粒子については、長軸長と短軸長との比率（長軸長／短軸長）を測定しなくてもよい。また、画像の端には、粒子全体が画像に収まっていない非磁性粒子が観察される場合もあるが、そのような非磁性粒子も測定対象外とする。
以上により、各画像において、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下であるすべての非磁性粒子を特定する。
（５）比率ｂ／ｔの平均値の算出
上記（４）で特定した長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である各非磁性粒子の輪郭上の、磁性層と非磁性層との界面との直線距離が最も短い位置を特定し、この位置と磁性層と非磁性層との界面との直線距離を「ｃ」とする。この非磁性粒子を含む画像について、上記（３）で求めた磁性層の厚みｔの値から「ｃ」を差し引いた値を、埋没深さｂとする（即ち、「ｔ−ｃ」＝ｂ）。なお磁性層側表面から突出せずに磁性層に完全に埋没している非磁性粒子についても、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下であれば、上記方法で埋没深さｂを求めることとする。そして、求めたｂの値を、この非磁性粒子を含む画像について、上記（３）で求めた磁性層の厚みｔで除して、ｂ／ｔを算出する。
以上のｂ／ｔの算出を、撮像した４画像において特定された長軸長と短軸長との比率（長軸長／短軸長）が１．５以下であるすべての非磁性粒子について行い、得られた値の算術平均を、比率ｂ／ｔの平均値とする。
ここで、ｂ、ｃ、ｔは、すべて同一単位の値とする。例えば単位としてμｍを採用するならば、ｂ、ｃ、ｔはすべて単位μｍの数値とし、単位としてｎｍを採用するならば、ｂ、ｃ、ｔはすべて単位ｎｍの数値とする。同一単位を採用する点は、長軸長と短軸長との比率（長軸長／短軸長）を求める際も同様である。
(Measuring method)
The average value of the ratio b / t described above is obtained by the following method. In the following, a measurement in a magnetic recording medium having a nonmagnetic layer on a nonmagnetic support and a magnetic layer on the nonmagnetic layer will be described as an example. However, the magnetic recording medium may be a magnetic recording medium having a magnetic layer directly on a nonmagnetic support. In this case, the interface described below is the interface between the magnetic layer and the nonmagnetic support.
(1) Preparation of cross-section observation sample A cross-section observation sample is cut out from a randomly determined position of a target magnetic recording medium whose average value of the ratio b / t is obtained. The cross-sectional observation sample is manufactured by FIB (Focused Ion Beam) processing using a gallium ion (Ga + ) beam. Specific examples of such a manufacturing method will be described later with reference to examples.
(2) Identification of observation region The prepared cross-sectional observation sample is observed with an SEM, and a cross-sectional image (SEM image) is taken. As the scanning electron microscope, a field emission scanning electron microscope (FE (Field Emission) -SEM) is used. For example, FE-SEM S4800 manufactured by Hitachi, Ltd. can be used, and this FE-SEM was used in Examples described later.
The SEM image is the same sample for cross-sectional observation.
(I) Make sure that the areas to be imaged do not overlap
(Ii) The magnetic layer side surface (magnetic layer surface) and the nonmagnetic particles protruding on the magnetic layer side surface are contained in the SEM image, and (iii) the entire thickness direction of the magnetic layer of the sample for cross-sectional observation (that is, In the case where there are nonmagnetic particles penetrating the interface between the magnetic layer and the nonmagnetic layer), the nonmagnetic particles fit in the SEM image. like,
Except for the points to be selected, images are taken at randomly selected positions to obtain a total of four images. The SEM image is a secondary electron image (SE (secondary electron) image) captured at an acceleration voltage of 5 kV, an imaging magnification of 100,000 times, and 960 pixels (pixels) × 1280 pixels horizontally.
In the SEM image, the ferromagnetic powder and the non-magnetic powder (non-magnetic particles) can be easily distinguished from each other based on the difference in density on the image, the size, the shape, and the like. Non-magnetic particles are composed of components on the magnetic layer surface by energy dispersive X-ray spectroscopy (EDS), Auger Electron Spectroscopy (AES), and scanning electron microscope. It can also be analyzed by a known method capable of composition analysis such as mapping.
(3) Measurement of thickness t of magnetic layer The captured SEM image is taken into WinROOF manufactured by Mitani Shoji Co., Ltd., and the magnetic layer portion (observation region) in the SEM image is selected. In the selection of the observation region, the length in the width direction of the observation region is the full width of the captured SEM image. In addition, the width direction described regarding the SEM image refers to the width direction of the imaged cross-sectional observation sample. The width direction in the cross-section observation sample is the width direction in the magnetic recording medium from which the sample is cut. The same applies to the thickness direction.
Regarding the thickness direction, the interface between the magnetic layer and the nonmagnetic layer is specified by the following method. The SEM image is digitized to create image luminance data in the thickness direction (consisting of three components: thickness direction coordinates, width direction coordinates, and luminance). In digitization, the SEM image is divided into 1280 in the width direction and processed with 8-bit luminance to obtain 256 gradation data, and the image luminance of each divided coordinate point is converted into a predetermined gradation value. Next, in the obtained image luminance data, the average value of the luminance in the width direction at each coordinate point in the thickness direction (that is, the average value of the luminance at each coordinate point divided by 1280) is taken as the vertical axis, and the coordinate in the thickness direction is Create a brightness curve for the horizontal axis. A differential curve is created by differentiating the created luminance curve, and the coordinates of the boundary between the magnetic layer and the nonmagnetic layer are specified from the peak position of the created differential curve. A position corresponding to the specified coordinates on the SEM image is defined as an interface between the magnetic layer and the nonmagnetic layer.
The surface on the magnetic layer side is also specified using a luminance curve in the same manner as described above.
Obtain the shortest straight line distance between the specified magnetic layer side surface and the interface between the magnetic layer and the nonmagnetic layer at an arbitrary position in each of the four captured images, and average the values obtained in the four images Is the thickness t of the magnetic layer. In the present invention and this specification, the average value means an arithmetic average.
(4) Identification of nonmagnetic particles having a major axis length / minor axis length ratio (major axis length / minor axis length) of 1.5 or less A portion of nonmagnetic particles in each of the four images taken. The major axis length and the minor axis length are determined by image analysis from the image luminance data. Specifically, each image (SEM image) is digitized, and image luminance data in the major axis direction and minor axis direction of the nonmagnetic particles (major axis direction coordinates, minor axis direction coordinates, and luminance three components). Create. In digitization, the SEM image is divided into 1280 in the width direction and processed with 8-bit luminance to obtain 256 gradation data, and the image luminance of each divided coordinate point is converted into a predetermined gradation value. Next, in the obtained image luminance data, the horizontal axis is the coordinate in the direction corresponding to the major axis of the particle, and the average value of the luminance at each coordinate point in the major axis direction (that is, the average value of the luminance at each coordinate point divided by 1280) ) On the vertical axis to create a luminance curve. A differential curve is created by differentiating the created luminance curve, and the coordinates of the boundary of the nonmagnetic particle portion are specified from the peak position of the created differential curve. The operation of taking the coordinate in the direction corresponding to the major axis of the particle as the horizontal axis is repeated three times, and the longest axial length is defined as the major axis length. The operation of taking the coordinate on the horizontal axis in the short axis direction is repeated three times, and the shortest axis length is defined as the short axis length. Specifically, the long axis length is determined by setting an axis (straight line) that can take the longest particle as the long axis, and is the length of the long axis. On the other hand, the short axis is determined as the axis having the longest length when the particle length is taken along a straight line orthogonal to the long axis, and the length of this axis is defined as the short axis length. However, indeterminate non-magnetic particles whose major axis and / or minor axis constituting the particles cannot be specified from the shape are excluded from measurement. In addition, the ratio of the major axis length to the minor axis length is apparent for non-magnetic particles at a glance that the ratio of the major axis length to the minor axis length (major axis length / minor axis length) exceeds 1.5. It is not necessary to measure (long axis length / short axis length). Further, non-magnetic particles in which the entire particles are not included in the image may be observed at the edge of the image, but such non-magnetic particles are also excluded from the measurement target.
As described above, in each image, all non-magnetic particles having a ratio of major axis length to minor axis length (major axis length / minor axis length) of 1.5 or less are specified.
(5) Calculation of average value of ratio b / t Each nonmagnetic particle having a ratio of the major axis length to the minor axis length (major axis length / minor axis length) specified in (4) above of 1.5 or less. The position on the contour where the linear distance between the interface between the magnetic layer and the nonmagnetic layer is shortest is specified, and the linear distance between this position and the interface between the magnetic layer and the nonmagnetic layer is defined as “c”. For the image including the nonmagnetic particles, a value obtained by subtracting “c” from the value of the thickness t of the magnetic layer obtained in the above (3) is set as an embedded depth b (that is, “t−c” = b). . Note that the ratio of the major axis length to the minor axis length (major axis length / minor axis length) is 1.5 or less even for nonmagnetic particles that are completely embedded in the magnetic layer without protruding from the surface on the magnetic layer side. If there is, the buried depth b is obtained by the above method. Then, b / t is calculated by dividing the obtained value b by the thickness t of the magnetic layer obtained in (3) above for the image containing the non-magnetic particles.
The above b / t is calculated for all non-magnetic particles having a ratio of the major axis length to the minor axis length (major axis length / minor axis length) specified in the four captured images of 1.5 or less. The arithmetic average of the obtained values is taken as the average value of the ratio b / t.
Here, b, c, and t are all values of the same unit. For example, if μm is used as the unit, b, c, and t are all numerical values in the unit μm, and if nm is used as the unit, b, c, and t are all numerical values in the unit nm. The same unit is adopted when the ratio of the major axis length to the minor axis length (major axis length / minor axis length) is obtained.
＜突起の個数＞
上記磁気記録媒体は、磁性層に、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である複数個の非磁性粒子が、上記比率ｂ／ｔの平均値が０．９以下の状態で磁性層に存在し、更に、磁性層側の表面において原子間力顕微鏡（ＡＦＭ：Atomic Force Microscope）により測定される突起の個数が、面積４０μｍ×４０μｍあたり、高さ５ｎｍ以上の突起の個数が８００個以上であり、かつ高さ２０ｎｍ以上の突起の個数が２０個以下である。これにより、走行時の摩擦係数の低減と、電磁変換特性の更なる向上が可能になる。この点に関する本発明者による推察は、先に記載した通りである。以下に記載の突起の個数は、特記しない限り、面積４０μｍ×４０μｍあたりの個数をいうものとする。
高さ５ｎｍ以上の突起の個数は、面積４０μｍ×４０μｍあたり、８００個以上であり、走行時の摩擦係数の上昇をより効果的に抑制する観点から、９００個以上であることが好ましく、１０００個以上であることがより好ましく、２０００個以上であることが更に好ましく、３０００個以上であることが一層好ましく、４０００個以上であることがより一層好ましく、５０００個以上であることが更に一層好ましい。高さ５ｎｍ以上の突起の個数が多いほど、走行時の摩擦係数の上昇を抑制することができる。他方、高さ５ｎｍ以上の突起の個数は、面積４０μｍ×４０μｍあたり、例えば５００，０００個以下であることができるが、これを超えてもよい。
一方、高さ２０ｎｍ以上の突起の個数は、面積４０μｍ×４０μｍあたり、２０個以下であり、電磁変換特性のより一層の向上の観点からは、１５個以下であることが好ましく、１０個以下であることがより好ましく、５個以下であることが更に好ましく、３個以下であることが一層好ましく、０個であることがより一層好ましい。
<Number of protrusions>
In the magnetic recording medium, a plurality of nonmagnetic particles having a major axis length / minor axis length ratio (major axis length / minor axis length) of 1.5 or less are formed on the magnetic layer at the ratio b / t. The average value is 0.9 or less in the magnetic layer, and the number of protrusions measured on the surface of the magnetic layer by an atomic force microscope (AFM) is about 40 μm × 40 μm in area. The number of protrusions having a height of 5 nm or more is 800 or more, and the number of protrusions having a height of 20 nm or more is 20 or less. This makes it possible to reduce the friction coefficient during traveling and further improve the electromagnetic conversion characteristics. The inference by the present inventor regarding this point is as described above. The number of protrusions described below refers to the number per area of 40 μm × 40 μm unless otherwise specified.
The number of protrusions having a height of 5 nm or more is 800 or more per 40 μm × 40 μm area, and is preferably 900 or more from the viewpoint of more effectively suppressing an increase in the friction coefficient during running. More preferably, it is more preferably 2000 or more, still more preferably 3000 or more, still more preferably 4000 or more, and even more preferably 5000 or more. As the number of protrusions having a height of 5 nm or more increases, an increase in the friction coefficient during traveling can be suppressed. On the other hand, the number of projections having a height of 5 nm or more can be, for example, 500,000 or less per 40 μm × 40 μm area, but may exceed this.
On the other hand, the number of protrusions having a height of 20 nm or more is 20 or less per 40 μm × 40 μm area, and is preferably 15 or less from the viewpoint of further improving the electromagnetic conversion characteristics. More preferably, it is more preferably 5 or less, still more preferably 3 or less, and even more preferably 0.
（測定方法）
以上記載した突起の個数は、以下の方法により求めるものとする。
ＡＦＭによって測定された、視野中の凸成分と凹成分の体積が等しくなる面を基準面として定め、測定対象の磁気記録媒体の磁性層側表面の無作為に選択した５箇所の測定領域（各測定領域の面積：４０μｍ×４０μｍ）において、基準面から５ｎｍ以上の高さの部分を高さ５ｎｍ以上の突起、基準面から２０ｎｍ以上の高さの部分を高さ２０ｎｍ以上の高さの突起とし、測定領域内のそれぞれの突起の個数を求める。測定領域の端には、全体が測定領域に収まっていない突起も存在し得るが、そのような突起もカウントする。なお突起の個数は累積個数としてカウントされるため、高さ５ｎｍ以上の突起には、高さ２０ｎｍ以上の突起も含まれる。ＡＦＭによる測定条件の一例としては、下記の測定条件を挙げることができる。後述の実施例に示す突起の個数は、下記測定条件による測定によって上記５箇所で求めた測定値の平均値である。
ＡＦＭ（Ｖｅｅｃｏ社Ｎａｎｏｓｃｏｐｅ４）で磁気記録媒体の磁性層側表面の無作為に選択した面積４０μｍ×４０μｍの領域５箇所を測定する。スキャン速度（探針移動速度）は４０μｍ／ｓｅｃ、分解能は５１２ｐｉｘｅｌ×５１２ｐｉｘｅｌとする。
(Measuring method)
The number of protrusions described above is determined by the following method.
The surface measured by the AFM and having the same volume of the convex component and the concave component in the field of view is defined as a reference surface, and five measurement regions randomly selected on the magnetic layer side surface of the magnetic recording medium to be measured (each In the area of the measurement region: 40 μm × 40 μm), a portion having a height of 5 nm or more from the reference surface is a protrusion having a height of 5 nm or more, and a portion having a height of 20 nm or more from the reference surface is a protrusion having a height of 20 nm or more. Then, the number of each protrusion in the measurement region is obtained. Although there may be protrusions that are not entirely within the measurement area at the end of the measurement area, such protrusions are also counted. Since the number of protrusions is counted as a cumulative number, protrusions having a height of 5 nm or more include protrusions having a height of 20 nm or more. As an example of the measurement conditions by AFM, the following measurement conditions can be mentioned. The number of protrusions shown in the examples described later is an average value of measured values obtained at the above five locations by measurement under the following measurement conditions.
Five regions of a randomly selected area of 40 μm × 40 μm are measured on the magnetic layer side surface of the magnetic recording medium by AFM (Veeco Nanoscope 4). The scanning speed (probe moving speed) is 40 μm / sec, and the resolution is 512 pixels × 512 pixels.
＜比率ｂ／ｔの平均値および突起の個数の調整方法＞
次に、上記で説明した各種値の調整方法について説明する。
上記の高さ５ｎｍ以上の突起の個数および高さ２０ｎｍ以上の突起の個数は、好ましくは、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である非磁性粒子の、磁気記録媒体の磁性層側表面からの突出状態によって、調整することができる。
一方、比率ｂ／ｔの平均値を０．９以下に調整するためには、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である非磁性粒子を、磁性層と隣接する非磁性支持体または非磁性層との界面近傍の領域に達するほど磁性層内部に埋没させないことが好ましい。この点に関して、前述の特許文献１に記載されているように磁性層の厚みに対してサイズが大きい非磁性粒子を磁性層内部に埋没させないようにするには、この非磁性粒子を磁気記録媒体の磁性層側表面から大きく突出させることとなる。しかし、これでは、突出した非磁性粒子が磁性層側表面において高さ２０ｎｍ以上の突起となり、高さ２０ｎｍ以上の突起の個数が２０個を超えてしまうと考えられる。他方、磁性層の厚みに対してサイズが小さな非磁性粒子を単に磁性層形成用組成物の成分として用いるのみでは、この非磁性粒子全体が磁性層に埋没してしまい、高さ５ｎｍ以上の突起の個数を８００個以上とすることは困難と考えられる。
以上の点について本発明者は鋭意検討を重ねた結果、特許文献１に記載されているほど磁性層厚みに対してサイズが大きくない非磁性粒子を用いて、この非磁性粒子を、磁気記録媒体の磁性層側表面に局在させ得る製造方法により磁気記録媒体を製造することにより、比率ｂ／ｔが０．９以下であり、かつ高さ５ｎｍ以上の突起の個数および高さ２０ｎｍ以上の突起の個数が、それぞれ上記範囲にある磁気記録媒体を得ることができると考えるに至った。この点から、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下の非磁性粒子の長軸長の平均値（平均長軸長）φの磁性層厚みｔに対する比率φ／ｔは、１．０以下であることが好ましく、０．８以下であることがより好ましく、０．６以下であることが更に好ましい。
なお近年、高密度記録化に伴い記録波長の短波長化が指向されている。記録波長の短波長化に伴い、磁気記録における最小記録単位であるビット長は小さくなる傾向にある。これに伴い、ビット体積（ビット長×磁性層厚み）中に含まれる非磁性粒子が電磁変換特性に与える影響は大きくなる。この点からも、磁性層厚み方向全域を非磁性粒子が占めないことは望ましい。
また、上記比率φ／ｔは、例えば０．１以上、０．２以上であることができるが。これらを下回ってもよい。なお、上記の長軸長の平均値（平均長軸長）φは、先に記載した方法でＳＥＭで撮像した４画像において特定した長軸長と短軸長との比率（長軸長／短軸長）が１．５以下のすべての非磁性粒子の長軸長の算術平均とする。磁性層の厚みｔは、先に記載した方法により求めた値を用いる。また、φ／ｔの算出にあたり、φとｔの単位は同一とする。
また、好ましい磁気記録媒体の製造方法の一例は、後述する。
<Adjustment method of average value of ratio b / t and number of protrusions>
Next, a method for adjusting the various values described above will be described.
The number of protrusions having a height of 5 nm or more and the number of protrusions having a height of 20 nm or more are preferably such that the ratio of the major axis length to the minor axis length (major axis length / minor axis length) is 1.5 or less. It can be adjusted by the protruding state of the non-magnetic particles from the surface of the magnetic recording medium on the magnetic layer side.
On the other hand, in order to adjust the average value of the ratio b / t to 0.9 or less, the ratio of the major axis length to the minor axis length (major axis length / minor axis length) is 1.5 or less. Is preferably not buried in the magnetic layer so as to reach a region near the interface between the nonmagnetic support or the nonmagnetic layer adjacent to the magnetic layer. In this regard, as described in the above-mentioned Patent Document 1, in order to prevent nonmagnetic particles having a size larger than the thickness of the magnetic layer from being embedded in the magnetic layer, the nonmagnetic particles are used as a magnetic recording medium. It protrudes greatly from the magnetic layer side surface. However, in this case, it is considered that the protruding nonmagnetic particles become protrusions having a height of 20 nm or more on the surface of the magnetic layer, and the number of protrusions having a height of 20 nm or more exceeds 20. On the other hand, if nonmagnetic particles having a small size with respect to the thickness of the magnetic layer are merely used as a component of the composition for forming the magnetic layer, the entire nonmagnetic particles are buried in the magnetic layer, resulting in protrusions having a height of 5 nm or more. It is considered difficult to make the number of the number 800 or more.
As a result of intensive studies on the above points, the present inventor has used non-magnetic particles that are not as large as the magnetic layer thickness as described in Patent Document 1, and used these non-magnetic particles as magnetic recording media. By manufacturing a magnetic recording medium by a manufacturing method that can be localized on the surface of the magnetic layer, the ratio b / t is 0.9 or less, the number of protrusions having a height of 5 nm or more, and the protrusion having a height of 20 nm or more. It has been considered that a magnetic recording medium in which the number of each is in the above range can be obtained. From this point, the magnetic layer thickness of the average value of the major axis length (average major axis length) φ of the nonmagnetic particles whose ratio of major axis length to minor axis length (major axis length / minor axis length) is 1.5 or less. The ratio φ / t to t is preferably 1.0 or less, more preferably 0.8 or less, and still more preferably 0.6 or less.
In recent years, the recording wavelength has been shortened with high density recording. As the recording wavelength becomes shorter, the bit length, which is the minimum recording unit in magnetic recording, tends to become smaller. Accordingly, the influence of nonmagnetic particles contained in the bit volume (bit length × magnetic layer thickness) on the electromagnetic conversion characteristics increases. Also from this point, it is desirable that the nonmagnetic particles do not occupy the entire magnetic layer thickness direction.
The ratio φ / t can be, for example, 0.1 or more and 0.2 or more. You may be less than these. Note that the average value of the long axis length (average long axis length) φ is the ratio of the long axis length and the short axis length specified in the four images captured by the SEM by the method described above (long axis length / short axis). The arithmetic average of the major axis lengths of all the nonmagnetic particles whose (axis length) is 1.5 or less. As the thickness t of the magnetic layer, the value obtained by the method described above is used. In calculating φ / t, the units of φ and t are the same.
An example of a preferable method for manufacturing a magnetic recording medium will be described later.
次に、本発明の一態様にかかる磁気記録媒体の磁性層、非磁性層等について、更に詳細に説明する。 Next, the magnetic layer, nonmagnetic layer, and the like of the magnetic recording medium according to one embodiment of the present invention will be described in more detail.
＜磁性層＞
（強磁性粉末）
強磁性粉末としては、磁気記録媒体の磁性層において通常用いられる各種強磁性粉末を使用することができる。強磁性粉末として平均粒子サイズの小さいものを使用することは、磁気記録媒体の記録密度向上の観点から好ましい。この点から、強磁性粉末としては、平均粒子サイズが５０ｎｍ以下の強磁性粉末を用いることが好ましい。一方、磁化の安定性の観点からは、強磁性粉末の平均粒子サイズは１０ｎｍ以上であることが好ましい。
<Magnetic layer>
(Ferromagnetic powder)
As the ferromagnetic powder, various ferromagnetic powders usually used in a magnetic layer of a magnetic recording medium can be used. It is preferable to use a ferromagnetic powder having a small average particle size from the viewpoint of improving the recording density of the magnetic recording medium. From this point, it is preferable to use a ferromagnetic powder having an average particle size of 50 nm or less as the ferromagnetic powder. On the other hand, from the viewpoint of magnetization stability, the average particle size of the ferromagnetic powder is preferably 10 nm or more.
強磁性粉末の好ましい具体例としては、強磁性六方晶フェライト粉末を挙げることができる。強磁性六方晶フェライト粉末の平均粒子サイズ（平均板径）は、記録密度向上と磁化の安定性の観点から、１０ｎｍ以上５０ｎｍ以下であることが好ましく、２０ｎｍ以上５０ｎｍ以下であることがより好ましい。強磁性六方晶フェライト粉末の詳細については、例えば、特開２０１１−２２５４１７号公報段落００１２〜００３０、特開２０１１−２１６１４９号公報の段落０１３４〜０１３６、特開２０１２−２０４７２６号公報段落００１３〜００３０を参照できる。 Preferable specific examples of the ferromagnetic powder include ferromagnetic hexagonal ferrite powder. The average particle size (average plate diameter) of the ferromagnetic hexagonal ferrite powder is preferably 10 nm or more and 50 nm or less, and more preferably 20 nm or more and 50 nm or less, from the viewpoint of improvement in recording density and magnetization stability. Details of the ferromagnetic hexagonal ferrite powder include, for example, paragraphs 0012 to 0030 of JP2011-225417A, paragraphs 0134 to 0136 of JP2011-216149A, paragraphs 0013 to 0030 of JP2012-204726A. You can refer to it.
強磁性粉末の好ましい具体例としては、強磁性金属粉末を挙げることもできる。強磁性金属粉末の平均粒子サイズ（平均長軸長）は、記録密度向上と磁化の安定性の観点から、１０ｎｍ以上５０ｎｍ以下であることが好ましく、２０ｎｍ以上５０ｎｍ以下であることがより好ましい。強磁性金属粉末の詳細については、例えば特開２０１１−２１６１４９号公報の段落０１３７〜０１４１、特開２００５−２５１３５１号公報段落０００９〜００２３を参照できる。 Preferable specific examples of the ferromagnetic powder include a ferromagnetic metal powder. The average particle size (average major axis length) of the ferromagnetic metal powder is preferably 10 nm or more and 50 nm or less, and more preferably 20 nm or more and 50 nm or less, from the viewpoint of improvement in recording density and magnetization stability. For details of the ferromagnetic metal powder, reference can be made, for example, to paragraphs 0137 to 0141 of JP2011-216149A and paragraphs 0009 to 0023 of JP2005-251351A.
本発明および本明細書において、特記しない限り、強磁性粉末等の各種粉末の平均粒子サイズは、透過型電子顕微鏡を用いて、以下の方法により測定される値とする。
粉末を、透過型電子顕微鏡を用いて撮影倍率１０００００倍で撮影し、総倍率５０００００倍になるように印画紙にプリントして粉末を構成する粒子の写真を得る。得られた粒子の写真から目的の粒子を選びデジタイザーで粒子の輪郭をトレースし粒子（一次粒子）のサイズを測定する。一次粒子とは、凝集のない独立した粒子をいう。なお磁性層形成のために用いられる非磁性粒子の粒子サイズは、上記方法により測定される粒子サイズである。
以上の測定を、無作為に抽出した５００個の粒子について行う。こうして得られた５００個の粒子の粒子サイズの算術平均を、粉末の平均粒子サイズとする。上記透過型電子顕微鏡としては、例えば日立製透過型電子顕微鏡Ｈ−９０００型を用いることができる。また、粒子サイズの測定は、公知の画像解析ソフト、例えばカールツァイス製画像解析ソフトＫＳ−４００を用いて行うことができる。
本発明において、強磁性粉末およびその他の粉末についての平均粒子サイズとは、特記しない限り、上記方法により求められる平均粒子サイズをいうものとする。後述の実施例に示す平均粒子サイズの測定は、透過型電子顕微鏡として日立製透過型電子顕微鏡Ｈ−９０００型、画像解析ソフトとしてカールツァイス製画像解析ソフトＫＳ−４００を用いて行った。なお磁性層に含まれる長軸長と短軸長との比率（長軸長／短軸長）が１．５以下の非磁性粉末の平均長軸長φは、ＳＥＭ像において先に記載した方法により求められる値である。
In the present invention and the present specification, unless otherwise specified, the average particle size of various powders such as ferromagnetic powders is a value measured by the following method using a transmission electron microscope.
The powder is photographed at a photographing magnification of 100,000 using a transmission electron microscope, and printed on photographic paper so that the total magnification is 500,000 times to obtain a photograph of particles constituting the powder. The target particle is selected from the photograph of the obtained particle, the outline of the particle is traced with a digitizer, and the size of the particle (primary particle) is measured. Primary particles refer to independent particles without agglomeration. The particle size of the nonmagnetic particles used for forming the magnetic layer is the particle size measured by the above method.
The above measurements are performed on 500 randomly extracted particles. The arithmetic average of the particle sizes of the 500 particles thus obtained is taken as the average particle size of the powder. As the transmission electron microscope, for example, Hitachi transmission electron microscope H-9000 type can be used. The particle size can be measured using known image analysis software, for example, image analysis software KS-400 manufactured by Carl Zeiss.
In the present invention, the average particle size for the ferromagnetic powder and other powders means the average particle size determined by the above method unless otherwise specified. Measurement of the average particle size shown in Examples described later was performed using a Hitachi transmission electron microscope H-9000 type as a transmission electron microscope and Carl Zeiss image analysis software KS-400 as image analysis software. The average major axis length φ of the nonmagnetic powder having a major axis length / minor axis length ratio (major axis length / minor axis length) included in the magnetic layer of 1.5 or less is the method described above in the SEM image. Is a value obtained by
粒子サイズ測定のために磁気記録媒体から試料粉末を採取する方法としては、例えば特開２０１１−０４８８７８号公報の段落００１５に記載の方法を採用することができる。 As a method for collecting the sample powder from the magnetic recording medium for the particle size measurement, for example, the method described in paragraph 0015 of JP2011-048878A can be employed.
本発明および本明細書において、特記しない限り、粉末を構成する粒子のサイズ（粒子サイズ）は、上記の粒子写真において観察される粒子の形状が、
（１）針状、紡錘状、柱状（ただし、高さが底面の最大長径より大きい）等の場合は、粒子を構成する長軸の長さ、即ち長軸長で表され、
（２）板状または柱状（ただし、厚みまたは高さが板面または底面の最大長径より小さい）場合は、その板面または底面の最大長径で表され、
（３）球形、多面体状、不特定形等であって、かつ形状から粒子を構成する長軸を特定できない場合は、円相当径で表される。円相当径とは、円投影法で求められるものを言う。
In the present invention and the present specification, unless otherwise specified, the size of the particles constituting the powder (particle size) is the shape of the particles observed in the above particle photograph,
(1) In the case of needle shape, spindle shape, columnar shape (however, the height is larger than the maximum major axis of the bottom surface), it is represented by the length of the major axis constituting the particle, that is, the major axis length,
(2) In the case of a plate or columnar shape (however, the thickness or height is smaller than the maximum major axis of the plate surface or bottom surface), it is represented by the maximum major axis of the plate surface or bottom surface,
(3) In the case of a spherical shape, a polyhedral shape, an unspecified shape, etc., and the major axis constituting the particle cannot be specified from the shape, it is represented by an equivalent circle diameter. The equivalent circle diameter is a value obtained by a circle projection method.
また、粉末の平均針状比は、上記測定において粒子の短軸の長さ、即ち短軸長を測定し、各粒子の（長軸長／短軸長）の値を求め、上記５００個の粒子について得た値の算術平均を指す。ここで、特記しない限り、短軸長とは、上記粒子サイズの定義で（１）の場合は、粒子を構成する短軸の長さを、同じく（２）の場合は、厚みまたは高さを各々指し、（３）の場合は、長軸と短軸の区別がないから、（長軸長／短軸長）は、便宜上１とみなす。
そして、特記しない限り、粒子の形状が特定の場合、例えば、上記粒子サイズの定義（１）の場合、平均粒子サイズは平均長軸長であり、同定義（２）の場合、平均粒子サイズは平均板径であり、平均板状比とは、（最大長径／厚みまたは高さ）の算術平均である。同定義（３）の場合、平均粒子サイズは、平均直径（平均粒径、平均粒子径ともいう）である。
The average acicular ratio of the powder is determined by measuring the length of the minor axis of the particle, that is, the minor axis length in the above measurement, and obtaining the value of (major axis length / minor axis length) of each particle. Refers to the arithmetic average of the values obtained for the particles. Here, unless otherwise specified, the minor axis length is the definition of the particle size in the case of (1), the length of the minor axis constituting the particle, and in the case of (2), the thickness or height. In the case of (3), since there is no distinction between the major axis and the minor axis, (major axis length / minor axis length) is regarded as 1 for convenience.
Unless otherwise specified, when the shape of the particle is specific, for example, in the case of definition (1) of the particle size, the average particle size is the average major axis length, and in the case of definition (2), the average particle size is The average plate diameter is an arithmetic average of (maximum major axis / thickness or height). In the case of the same definition (3), the average particle size is an average diameter (also referred to as an average particle diameter or an average particle diameter).
磁性層における強磁性粉末の含有量（充填率）は、好ましくは５０〜９０質量％の範囲であり、より好ましくは６０〜９０質量％の範囲である。上記充填率が高いことは、記録密度向上の観点から好ましい。 The content (filling rate) of the ferromagnetic powder in the magnetic layer is preferably in the range of 50 to 90% by mass, more preferably in the range of 60 to 90% by mass. A high filling factor is preferable from the viewpoint of improving the recording density.
（結合剤）
上記磁気記録媒体は、磁性層に、強磁性粉末とともに結合剤を含む。結合剤としては、ポリウレタン樹脂、ポリエステル樹脂、ポリアミド樹脂、塩化ビニル樹脂、スチレン、アクリロニトリル、メチルメタクリレートなどを共重合したアクリル樹脂、ニトロセルロースなどのセルロース樹脂、エポキシ樹脂、フェノキシ樹脂、ポリビニルアセタール、ポリビニルブチラールなどのポリビニルアルキラール樹脂などから単独または複数の樹脂を混合して用いることができる。これらの中で好ましいものはポリウレタン樹脂、アクリル樹脂、セルロース樹脂、塩化ビニル樹脂である。なおこれらの樹脂は、ホモポリマーでもよく、コポリマー（共重合体）でもよい。これらの樹脂は、非磁性層や後述するバックコート層においても結合剤として使用することができる。以上の結合剤については、特開２０１０−２４１１３号公報段落００２８〜００３１を参照できる。また、上記結合剤として使用可能な樹脂とともに硬化剤を使用することもできる。硬化剤とは、１分子中に少なくとも１つ、好ましくは２つ以上の架橋性官能基を有する化合物である。硬化剤としては、ポリイソシアネートが好適である。ポリイソシアネートの詳細については、特開２０１１−２１６１４９号公報段落０１２４〜０１２５を参照できる。硬化剤は、結合剤１００．０質量部に対して例えば０〜８０．０質量部、磁性層等の各層の強度向上の観点からは好ましくは５０．０〜８０．０質量部の量で使用することができる。
(Binder)
The magnetic recording medium includes a binder in a magnetic layer together with a ferromagnetic powder. As binders, polyurethane resin, polyester resin, polyamide resin, vinyl chloride resin, acrylic resin copolymerized with styrene, acrylonitrile, methyl methacrylate, cellulose resin such as nitrocellulose, epoxy resin, phenoxy resin, polyvinyl acetal, polyvinyl butyral A single or a plurality of resins can be used in combination such as a polyvinyl alkyl resin such as the above. Among these, preferred are polyurethane resin, acrylic resin, cellulose resin, and vinyl chloride resin. These resins may be homopolymers or copolymers (copolymers). These resins can also be used as a binder in the nonmagnetic layer and the backcoat layer described later. JP, 2010-24113, A paragraphs 0028-0031 can be referred to for the above binder. Moreover, a hardening | curing agent can also be used with resin which can be used as the said binder. The curing agent is a compound having at least one, preferably two or more crosslinkable functional groups in one molecule. A polyisocyanate is suitable as the curing agent. JP, 2011-216149, A paragraphs 0124-0125 can be referred to for the details of polyisocyanate. The curing agent is used in an amount of, for example, 0 to 80.0 parts by mass with respect to 100.0 parts by mass of the binder, preferably 50.0 to 80.0 parts by mass from the viewpoint of improving the strength of each layer such as a magnetic layer. can do.
（長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である非磁性粒子）
上記磁気記録媒体は、磁性層に、強磁性粉末、結合剤とともに、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である非磁性粒子を複数個含む。かかる非磁性粒子が、比率ｂ／ｔの平均値が０．９以下の状態で磁性層に存在し、かつ磁性層側表面における高さ５ｎｍ以上の突起および高さ２０ｎｍ以上の突起の個数が、それぞれ上記範囲であることにより、走行時の摩擦係数を低減し、かつ優れた電磁変換特性を得ることが可能になる。上記非磁性粒子の長軸長と短軸長との比率（長軸長／短軸長）は、好ましくは１．３以下であり、より好ましくは１．１以下であり、１．０であってもよい。なお上記非磁性粒子の長軸長と短軸長との比率（長軸長／短軸長）が１．０である場合、かかる粒子は長軸長と短軸長とが等しい、即ち球状の粒子である。
(Nonmagnetic particles having a ratio of major axis length to minor axis length (major axis length / minor axis length) of 1.5 or less)
In the magnetic recording medium, a plurality of nonmagnetic particles having a major axis length / minor axis length ratio (major axis length / minor axis length) of 1.5 or less, together with a ferromagnetic powder and a binder, in a magnetic layer. Including. Such nonmagnetic particles are present in the magnetic layer in a state where the average value of the ratio b / t is 0.9 or less, and the number of protrusions having a height of 5 nm or more and a protrusion having a height of 20 nm or more on the surface of the magnetic layer is as follows. By being each in the said range, it becomes possible to reduce the friction coefficient at the time of driving | running | working and to obtain the outstanding electromagnetic conversion characteristic. The ratio of the major axis length to the minor axis length (major axis length / minor axis length) of the nonmagnetic particles is preferably 1.3 or less, more preferably 1.1 or less, and 1.0. May be. When the ratio of the major axis length to the minor axis length (major axis length / minor axis length) of the non-magnetic particle is 1.0, the major axis length and the minor axis length are equal to each other, that is, spherical. Particles.
上記非磁性粒子の平均長軸長φは、先に記載したように、磁性層の厚みｔに対して、比率φ／ｔが１．０以下であることが好ましい。また、平均長軸長φは、好ましくは１０〜１００ｎｍの範囲である。ただし、上記非磁性粒子を、比率ｂ／ｔの平均値が０．９以下の状態で磁性層に存在させることができればよく、平均長軸長φは上記範囲に限定されるものではない。 As described above, the average major axis length φ of the nonmagnetic particles is preferably such that the ratio φ / t is 1.0 or less with respect to the thickness t of the magnetic layer. The average major axis length φ is preferably in the range of 10 to 100 nm. However, it is only necessary that the nonmagnetic particles can be present in the magnetic layer in a state where the average value of the ratio b / t is 0.9 or less, and the average major axis length φ is not limited to the above range.
電磁変換特性のより一層の向上の観点からは、上記非磁性粒子の粒子サイズ（長軸長）のばらつきが少ないことは好ましい。長軸長のばらつきの程度は、変動係数（ＣＶ値；coefficientof variation）により評価することができる。ここでＣＶ値（単位：％）＝（σ／φ）×１００であり、φは上記の通り平均長軸長、σは長軸長の標準偏差である。長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である非磁性粒子のＣＶ値は、好ましくは３０．０％未満であり、より好ましくは１５．０％以下であり、更に好ましくは７．０％以下である。上記ＣＶ値は、例えば３．０％以上であるが、上記非磁性粒子の粒子サイズのばらつきが少ないほど好ましいため、これを下回ってもよい。ＣＶ値が小さい非磁性粒子としては、コロイド粒子が好ましい。なお本発明および本明細書におけるコロイド粒子とは、少なくとも、メチルエチルケトン、シクロヘキサノン、トルエンもしくは酢酸エチル、または上記溶媒の二種以上を任意の混合比で含む混合溶媒の少なくとも１つの有機溶媒１００ｍＬあたり１ｇ添加した際に、沈降せず分散しコロイド分散体をもたらすことのできる粒子をいうものとする。
磁性層に含まれる非磁性粒子がコロイド粒子であることは、磁性層の形成に用いた非磁性粒子が入手可能であれば、かかる非磁性粒子が、上記のコロイド粒子の定義に当てはまる性質を有するかを評価すればよい。または、磁性層から取りだした非磁性粒子が、上記のコロイド粒子の定義に当てはまる性質を有するかを評価することもできる。磁性層からの非磁性粒子の取り出しは、例えば、以下の方法で行うことができる。
１．磁性層を約１ｇ削り取る。削り取りは、例えば、かみそり刃などにより行うことができる。
２．削り取って得られた磁性層試料を、ナスフラスコ等の容器に入れ、この容器にテトラヒドロフランを１００ｍｌ添加する。なおテトラヒドロフランは、安定剤を添加し市販されているものと安定剤無添加で市販されているものがあるが、安定剤無添加のテトラヒドロフランを用いる。以下に記載の洗浄に用いるテトラヒドロフランについても、同様である。
３．上記容器に還流管を取り付けて、水温６０℃の湯浴において９０分間加熱する。加熱後の容器内の内容物をろ紙によりろ過後、ろ紙上に残った固形分を数回テトラヒドロフランで洗浄し、洗浄後の固形分をビーカー等の容器に移す。この容器に４Ｎ（４ｍｏｌ／Ｌ）塩酸水溶液を添加して溶解せずに残った残渣をフィルタろ過により取り出す。フィルタとしては、孔径が０．０５μｍより小さいものを用いる。例えば、クロマトグラフィー分析用に使用されるメンブレンフィルタ (例えば、メルク社製のＭＦミリポア)を用いることができる。フィルタろ過により取り出した残渣は、数回、純水で洗浄後、乾燥させる。
上記操作により強磁性粉末および有機物（結合剤等）が溶解され、非磁性粒子が残渣として回収される。
以上の工程により、磁性層から非磁性粒子を取り出すことができる。こうして取り出した非磁性粒子の中に、複数種の非磁性粒子が含まれている場合には、密度の違いによって複数種の非磁性粒子を分別することができる。
From the viewpoint of further improving the electromagnetic conversion characteristics, it is preferable that there is little variation in the particle size (major axis length) of the nonmagnetic particles. The degree of variation in the major axis length can be evaluated by a coefficient of variation (CV value). Here, the CV value (unit:%) = (σ / φ) × 100, φ is the average major axis length as described above, and σ is the standard deviation of the major axis length. The CV value of non-magnetic particles having a ratio of major axis length to minor axis length (major axis length / minor axis length) of 1.5 or less is preferably less than 30.0%, more preferably 15.0. % Or less, and more preferably 7.0% or less. The CV value is, for example, 3.0% or more. However, the smaller the non-magnetic particle size variation, the better. As the nonmagnetic particles having a small CV value, colloidal particles are preferable. The colloidal particles in the present invention and the present specification are added at least 1 g per 100 mL of at least one organic solvent of methyl ethyl ketone, cyclohexanone, toluene or ethyl acetate, or a mixed solvent containing two or more of the above solvents in an arbitrary mixing ratio. In this case, the particles that can be dispersed without being settled to give a colloidal dispersion.
The fact that the nonmagnetic particles contained in the magnetic layer are colloidal particles means that, if the nonmagnetic particles used to form the magnetic layer are available, such nonmagnetic particles have a property that falls within the definition of colloidal particles described above. You should evaluate. Alternatively, it is possible to evaluate whether the nonmagnetic particles taken out from the magnetic layer have properties that meet the definition of the colloidal particles. Extraction of nonmagnetic particles from the magnetic layer can be performed, for example, by the following method.
1. About 1 g of the magnetic layer is scraped off. The scraping can be performed with, for example, a razor blade.
2. The magnetic layer sample obtained by scraping is put into a container such as an eggplant flask, and 100 ml of tetrahydrofuran is added to the container. Tetrahydrofuran is commercially available with a stabilizer added and commercially available without a stabilizer, but tetrahydrofuran without a stabilizer is used. The same applies to tetrahydrofuran used for washing described below.
3. A reflux tube is attached to the container and heated in a hot water bath having a water temperature of 60 ° C. for 90 minutes. After filtering the contents in the heated container with a filter paper, the solid content remaining on the filter paper is washed several times with tetrahydrofuran, and the washed solid content is transferred to a container such as a beaker. A 4N (4 mol / L) aqueous hydrochloric acid solution is added to this container, and the residue that remains undissolved is removed by filtration. A filter having a pore diameter smaller than 0.05 μm is used. For example, a membrane filter (for example, MF Millipore manufactured by Merck) used for chromatographic analysis can be used. The residue taken out by filter filtration is washed several times with pure water and then dried.
By the above operation, the ferromagnetic powder and the organic substance (binder, etc.) are dissolved, and the nonmagnetic particles are recovered as a residue.
Through the above steps, the nonmagnetic particles can be taken out from the magnetic layer. In the case where a plurality of types of nonmagnetic particles are contained in the nonmagnetic particles thus taken out, the plurality of types of nonmagnetic particles can be separated according to the difference in density.
なお磁性層成分として、磁気記録媒体の磁性層側表面に突起を形成するために用いる非磁性粒子（いわゆる突起形成剤）について、先に記載した各種粉末の平均粒子サイズの測定方法により測定される平均粒子サイズ、この測定方法により測定された値から求められる変動係数ＣＶ値も、ＳＥＭにより撮像される断面画像を観察することで求められる各種値について上述した範囲にあることが好ましい。 As the magnetic layer component, nonmagnetic particles (so-called protrusion forming agents) used for forming protrusions on the magnetic layer side surface of the magnetic recording medium are measured by the above-described method for measuring the average particle size of various powders. It is preferable that the variation coefficient CV value obtained from the average particle size and the value measured by this measuring method is also in the above-described range for various values obtained by observing a cross-sectional image captured by the SEM.
長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である非磁性粒子は、無機粒子であっても有機粒子であってもよく、無機粒子が好ましい。無機粒子としては、金属酸化物、金属炭酸塩、金属硫酸塩、金属窒化物、金属炭化物、金属硫化物等の粒子を挙げることができる。具体例としては、α化率９０％以上のα−アルミナ、β−アルミナ、γ−アルミナ、θ−アルミナ、二酸化珪素等の珪素酸化物、炭化ケイ素、酸化クロム、酸化セリウム、α−酸化鉄、ゲータイト、コランダム、窒化珪素、チタンカーバイト、二酸化チタン、酸化スズ、酸化マグネシウム、酸化タングステン、酸化ジルコニウム、窒化ホウ素、酸化亜鉛、炭酸カルシウム、硫酸カルシウム、硫酸バリウム、二硫化モリブデン等の一種またはこれらの二種以上の複合酸化物等を挙げることができる。無機粒子としては、無機酸化物粒子が好ましく、珪素酸化物粒子がより好ましい。 Nonmagnetic particles having a major axis length / minor axis length ratio (major axis length / minor axis length) of 1.5 or less may be inorganic particles or organic particles, and inorganic particles are preferred. Examples of the inorganic particles include particles of metal oxide, metal carbonate, metal sulfate, metal nitride, metal carbide, metal sulfide and the like. Specific examples include α-alumina, β-alumina, γ-alumina, θ-alumina, silicon oxide such as silicon dioxide, silicon carbide, chromium oxide, cerium oxide, α-iron oxide having an α conversion rate of 90% or more, Goethite, corundum, silicon nitride, titanium carbide, titanium dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, etc. or one of these Two or more kinds of complex oxides can be exemplified. As the inorganic particles, inorganic oxide particles are preferable, and silicon oxide particles are more preferable.
先に記載したように、上記非磁性粒子の好ましい一態様は、コロイド粒子である。コロイド粒子としては、入手容易性の点から無機コロイド粒子が好ましく、無機酸化物コロイド粒子がより好ましい。無機酸化物コロイド粒子としては、上記無機酸化物のコロイド粒子を挙げることができ、ＳｉＯ2・Ａｌ2Ｏ3、ＳｉＯ2・Ｂ2Ｏ3、ＴｉＯ2・ＣｅＯ2、ＳｎＯ2・Ｓｂ2Ｏ3、ＳｉＯ2・Ａｌ2Ｏ3・ＴｉＯ2、ＴｉＯ2・ＣｅＯ2・ＳｉＯ2等の複合無機酸化物コロイド粒子を挙げることもできる。好ましいものとしては、ＳｉＯ2、Ａｌ2Ｏ3、ＴｉＯ2、ＺｒＯ2、Ｆｅ2Ｏ3などの無機酸化物コロイド粒子を挙げることができ、シリカコロイド粒子（コロイダルシリカ）が特に好ましい。ところで、一般的なコロイド粒子は表面が親水性であるため水を分散媒とするコロイド溶液の作製に適する。例えば一般的な合成法により得られるコロイダルシリカは、表面が分極した酸素原子（Ｏ2-）で覆われているため水中で水を吸着してヒドロキシル基を形成して安定化している。しかしこれら粒子は、磁性層形成用組成物に通常用いられる有機溶媒中では、コロイド状態で存在することは困難である。これに対し、本発明および本明細書におけるコロイド粒子は、先に記載した有機溶媒１００ｍＬあたり１ｇ添加した際に、沈降せず分散しコロイド分散体をもたらすことのできる粒子をいう。かかるコロイド粒子は、表面処理により表面を疎水化する等の公知の方法により調製することができる。そのような疎水化処理の詳細については、例えば特開平５−２６９３６５号公報、特開平５−２８７２１３号公報、特開平２００７−６３１１７号公報等に記載されている。 As described above, a preferred embodiment of the nonmagnetic particles is colloidal particles. As the colloid particles, inorganic colloid particles are preferable from the viewpoint of availability, and inorganic oxide colloid particles are more preferable. Examples of the inorganic oxide colloidal particles include colloidal particles of the above inorganic oxides, such as SiO 2 · Al 2 O 3 , SiO 2 · B 2 O 3 , TiO 2 · CeO 2 , SnO 2 · Sb 2 O 3. Further, composite inorganic oxide colloidal particles such as SiO 2 · Al 2 O 3 · TiO 2 , TiO 2 · CeO 2 · SiO 2 and the like can also be mentioned. Preferable examples include inorganic oxide colloidal particles such as SiO 2 , Al 2 O 3 , TiO 2 , ZrO 2 , and Fe 2 O 3 , and silica colloidal particles (colloidal silica) are particularly preferable. By the way, since a general colloidal particle has a hydrophilic surface, it is suitable for preparing a colloidal solution using water as a dispersion medium. For example, colloidal silica obtained by a general synthesis method is stabilized by adsorbing water in water to form hydroxyl groups because the surface is covered with polarized oxygen atoms (O 2− ). However, it is difficult for these particles to exist in a colloidal state in an organic solvent usually used in a composition for forming a magnetic layer. On the other hand, the colloidal particles in the present invention and the present specification refer to particles that can be dispersed without being settled to give a colloidal dispersion when 1 g per 100 mL of the organic solvent described above is added. Such colloidal particles can be prepared by a known method such as hydrophobizing the surface by surface treatment. Details of such hydrophobization treatment are described in, for example, JP-A Nos. 5-269365, 5-287213, 2007-63117, and the like.
好ましいコロイド粒子であるシリカコロイド粒子（コロイダルシリカ）については、製造方法は、一般的に、水ガラス法とゾルゲル法の２種類が知られている。水ガラス法とは、原料に珪酸ソーダ（珪酸ナトリウム、いわゆる水ガラス）を用いて、これをイオン交換させることで活性珪酸を発生させ、そこで粒子成長させる方法である。一方、ゾルゲル法は、テトラアルコキシシランを原料として用い、塩基性触媒下で加水分解させるのと同時に粒子成長させる方法である。上記非磁性粒子としてシリカコロイド粒子を用いる場合、シリカコロイド粒子は、いずれの製造方法で製造されたものであってもよい。 Regarding silica colloidal particles (colloidal silica), which is a preferred colloidal particle, two types of production methods are generally known: a water glass method and a sol-gel method. The water glass method is a method in which sodium silicate (sodium silicate, so-called water glass) is used as a raw material, ion-exchanged to generate active silicic acid, and particles are grown there. On the other hand, the sol-gel method is a method in which tetraalkoxysilane is used as a raw material and particles are grown simultaneously with hydrolysis under a basic catalyst. When silica colloid particles are used as the nonmagnetic particles, the silica colloid particles may be produced by any production method.
磁性層における、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である非磁性粒子の含有量は、好ましくは、強磁性粉末１００．０質量部に対して０．１〜１０．０質量部であり、より好ましくは０．１〜５．０質量部である。なお本発明において、ある成分は、一種のみ含まれていてもよく、構造や素材の異なる二種以上が含まれていてもよい。二種以上含まれる成分についての含有量とは、それら成分の合計含有量をいうものとする。なお磁性層には、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下の非磁性粒子が複数個含まれるが、その個数は特に限定されるものではない。 In the magnetic layer, the content of nonmagnetic particles having a major axis length / minor axis length ratio (major axis length / minor axis length) of 1.5 or less is preferably 100.0 parts by mass of the ferromagnetic powder. On the other hand, it is 0.1-10.0 mass part, More preferably, it is 0.1-5.0 mass part. In the present invention, a certain component may be included alone, or two or more different structures and materials may be included. The content of two or more components is the total content of these components. The magnetic layer includes a plurality of nonmagnetic particles having a ratio of the major axis length to the minor axis length (major axis length / minor axis length) of 1.5 or less, but the number is not particularly limited. Absent.
（添加剤）
上記磁気記録媒体の磁性層は、以上説明した各種成分を含み、任意に一種以上の添加剤を含むことができる。好ましい添加剤の一例としては、研磨剤を挙げることができる。研磨剤とは、走行中に磁気ヘッドに付着する付着物を除去する能力（研磨性）を発揮することができる成分である。更に、磁性層への研磨剤の添加により磁性層の強度を高める観点からは、研磨剤としては、形状が非等方的な粒子が好ましい。この点から、研磨剤としては、長軸長と短軸長との比率（長軸長／短軸長）が１．５超の非磁性粒子が好ましく、長軸長と短軸長との比率（長軸長／短軸長）１．５超５．０以下である非磁性粒子がより好ましい。なお研磨剤についての長軸長と短軸長との比率（長軸長／短軸長）は、先に長軸長と短軸長との比率（長軸長／短軸長）が１．５以下の非磁性粒子について記載したようにＳＥＭ像において求めるものとする。研磨剤の各粒子の長軸長は、例えば３０〜１００ｎｍの範囲であり、好ましくは５０〜１００ｎｍの範囲である。研磨剤としては、磁性層の研磨剤として通常使用される物質であるアルミナ（Ａｌ２Ｏ３）、炭化ケイ素、ボロンカーバイド（Ｂ４Ｃ）、ＳｉＯ２、ＴｉＣ、酸化クロム（Ｃｒ２Ｏ３）、酸化セリウム、酸化ジルコニウム（ＺｒＯ２）、酸化鉄、ダイヤモンドの各粒子を挙げることができ、中でもα−アルミナ等のアルミナ、炭化ケイ素、ダイヤモンドの各粒子が好ましい。磁性層の研磨剤含有量は、好ましくは強磁性粉末１００．０質量部に対して１．０〜２０．０質量部の範囲であり、より好ましくは３．０〜１５．０質量部の範囲であり、更に好ましくは４．０〜１０．０質量部の範囲である。
(Additive)
The magnetic layer of the magnetic recording medium contains the various components described above, and can optionally contain one or more additives. An example of a preferable additive is an abrasive. The abrasive is a component capable of exhibiting the ability (abrasiveness) to remove deposits adhering to the magnetic head during running. Furthermore, from the viewpoint of increasing the strength of the magnetic layer by adding an abrasive to the magnetic layer, the abrasive is preferably particles having an anisotropic shape. In this respect, as the abrasive, nonmagnetic particles having a ratio of the major axis length to the minor axis length (major axis length / minor axis length) of more than 1.5 are preferable, and the ratio of the major axis length to the minor axis length is preferred. Nonmagnetic particles having a major axis length / minor axis length of more than 1.5 and not more than 5.0 are more preferable. The ratio of the major axis length to the minor axis length (major axis length / minor axis length) of the abrasive is such that the ratio of the major axis length to the minor axis length (major axis length / minor axis length) is 1. It shall be determined in the SEM image as described for 5 or less non-magnetic particles. The major axis length of each particle of the abrasive is, for example, in the range of 30 to 100 nm, and preferably in the range of 50 to 100 nm. As the abrasive, alumina (Al 2 O 3 ), silicon carbide, boron carbide (B 4 C), SiO 2 , TiC, and chromium oxide (Cr 2 O 3 ), which are substances commonly used as abrasives for the magnetic layer, are used. , Cerium oxide, zirconium oxide (ZrO 2 ), iron oxide, and diamond particles. Among them, alumina particles such as α-alumina, silicon carbide particles, and diamond particles are preferable. The abrasive content of the magnetic layer is preferably in the range of 1.0 to 20.0 parts by mass, more preferably in the range of 3.0 to 15.0 parts by mass with respect to 100.0 parts by mass of the ferromagnetic powder. More preferably, it is the range of 4.0-10.0 mass parts.
磁性層に含まれ得る添加剤としては、更に、潤滑剤、分散剤・分散助剤、防黴剤、帯電防止剤、酸化防止剤等を挙げることができる。添加剤は、所望の性質に応じて市販品を適宜選択して使用することができる。 Examples of the additive that can be contained in the magnetic layer further include a lubricant, a dispersant / dispersion aid, an antifungal agent, an antistatic agent, and an antioxidant. As the additive, commercially available products can be appropriately selected and used according to desired properties.
以上説明した磁性層は、非磁性支持体上に直接、または非磁性層を介して設けることができる。非磁性層、非磁性支持体の詳細については、後述する。 The magnetic layer described above can be provided directly on the nonmagnetic support or via the nonmagnetic layer. Details of the nonmagnetic layer and the nonmagnetic support will be described later.
＜非磁性層＞
上記磁気記録媒体は、非磁性支持体上に直接磁性層を有することができ、または、非磁性支持体と磁性層との間に、非磁性粉末と結合剤を含む非磁性層を有することもできる。非磁性層に使用される非磁性粉末は、無機物質でも有機物質でもよい。また、カーボンブラック等も使用できる。無機物質としては、例えば金属、金属酸化物、金属炭酸塩、金属硫酸塩、金属窒化物、金属炭化物、金属硫化物等が挙げられる。これらの非磁性粉末は、市販品として入手可能であり、公知の方法で製造することもできる。その詳細については、特開２０１１−２１６１４９号公報段落０１４６〜０１５０を参照できる。非磁性層に使用可能なカーボンブラックについては、特開２０１０−２４１１３号公報段落００４０〜００４１も参照できる。非磁性層における非磁性粉末の含有量（充填率）は、好ましくは５０〜９０質量％の範囲であり、より好ましくは６０〜９０質量％の範囲である。
<Nonmagnetic layer>
The magnetic recording medium may have a magnetic layer directly on the nonmagnetic support, or may have a nonmagnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer. it can. The nonmagnetic powder used for the nonmagnetic layer may be an inorganic substance or an organic substance. Carbon black or the like can also be used. Examples of the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, and the like. These nonmagnetic powders are available as commercial products, and can also be produced by a known method. The details can be referred to paragraphs 0146 to 0150 of JP2011-216149A. JP, 2010-24113, A paragraphs 0040-0041 can also be referred to about carbon black which can be used for a nonmagnetic layer. The content (filling rate) of the nonmagnetic powder in the nonmagnetic layer is preferably in the range of 50 to 90 mass%, more preferably in the range of 60 to 90 mass%.
非磁性層の結合剤、添加剤等のその他詳細は、非磁性層に関する公知技術が適用できる。また、例えば、結合剤量および種類、添加剤量および種類に関しては、磁性層に関する公知技術も適用できる。 For other details such as binders and additives for the nonmagnetic layer, known techniques relating to the nonmagnetic layer can be applied. For example, with respect to the amount and type of the binder and the amount and type of the additive, known techniques relating to the magnetic layer can be applied.
なお、本発明において、磁気記録媒体の非磁性層には、非磁性粉末とともに、例えば不純物として、または意図的に、少量の強磁性粉末を含む実質的に非磁性な層も包含されるものとする。ここで実質的に非磁性な層とは、この層の残留磁束密度が１０ｍＴ以下であるか、保磁力が７．９６ｋＡ／ｍ（１００Ｏｅ）以下であるか、または、残留磁束密度が１０ｍＴ以下であり、かつ保磁力が７．９６ｋＡ／ｍ（１００Ｏｅ）以下である層をいうものとする。非磁性層は、残留磁束密度および保磁力を持たないことが好ましい In the present invention, the non-magnetic layer of the magnetic recording medium includes a substantially non-magnetic layer containing a small amount of ferromagnetic powder together with the non-magnetic powder, for example, as an impurity or intentionally. To do. Here, the substantially non-magnetic layer means that the residual magnetic flux density of this layer is 10 mT or less, the coercive force is 7.96 kA / m (100 Oe) or less, or the residual magnetic flux density is 10 mT or less. And a layer having a coercive force of 7.96 kA / m (100 Oe) or less. The nonmagnetic layer preferably has no residual magnetic flux density and coercive force.
＜バックコート層＞
上記磁気記録媒体は、非磁性支持体の磁性層を有する側とは反対側に、非磁性粉末および結合剤を含むバックコート層を有することもできる。バックコート層には、カーボンブラックおよび無機粉末の一方または両方が含有されていることが好ましい。バックコート層に含まれる結合剤、任意に含まれ得る各種添加剤については、磁性層や非磁性層の処方に関する公知技術を適用することができる。
<Back coat layer>
The magnetic recording medium can also have a backcoat layer containing nonmagnetic powder and a binder on the side opposite to the side having the magnetic layer of the nonmagnetic support. The back coat layer preferably contains one or both of carbon black and inorganic powder. With respect to the binder contained in the backcoat layer and various additives that can be optionally contained, known techniques relating to the formulation of the magnetic layer and the nonmagnetic layer can be applied.
＜非磁性支持体＞
次に、非磁性支持体について説明する。非磁性支持体としては、二軸延伸を行ったポリエチレンテレフタレート、ポリエチレンナフタレート、ポリアミド、ポリアミドイミド、芳香族ポリアミド等の公知のものが挙げられる。これらの中でもポリエチレンテレフタレート、ポリエチレンナフタレート、ポリアミドが好ましい。これらの支持体はあらかじめコロナ放電、プラズマ処理、易接着処理、熱処理などを行ってもよい。
<Non-magnetic support>
Next, the nonmagnetic support will be described. Examples of the nonmagnetic support include known ones such as biaxially stretched polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamideimide, and aromatic polyamide. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferable. These supports may be subjected in advance to corona discharge, plasma treatment, easy adhesion treatment, heat treatment and the like.
＜非磁性支持体および各層の厚み＞
上記磁気記録媒体における非磁性支持体および各層の厚みについては、非磁性支持体の厚みは、例えば３．００〜８０．００μｍの範囲であり、好ましくは３．００〜５０．００μｍの範囲であり、より好ましくは３．００〜１０．００μｍの範囲である。
<Nonmagnetic support and thickness of each layer>
Regarding the thickness of the nonmagnetic support and each layer in the magnetic recording medium, the thickness of the nonmagnetic support is, for example, in the range of 3.00 to 80.00 μm, and preferably in the range of 3.00 to 50.00 μm. More preferably, it is in the range of 3.00 to 10.00 μm.
磁性層の厚みについては、近年求められている高密度記録化の観点からは、磁性層の厚みは１００ｎｍ以下であることが好ましい。なお磁性層の厚みは、先に記載した方法により求められる。その他の層や非磁性支持体の厚みは、磁性層の厚みと同様の方法によって求めてもよく、公知の膜厚測定法により求めてもよい。または、塗布条件等の製造条件から算出される設計厚みとして求めてもよい。磁性層の厚みは、より好ましくは
１０ｎｍ〜１００ｎｍの範囲であり、更に好ましくは２０〜９０ｎｍの範囲である。磁性層は少なくとも一層あればよく、磁性層を異なる磁気特性を有する２層以上に分離してもかまわず、公知の重層磁性層に関する構成が適用できる。
As for the thickness of the magnetic layer, it is preferable that the thickness of the magnetic layer is 100 nm or less from the viewpoint of high density recording that has been required in recent years. The thickness of the magnetic layer is determined by the method described above. The thicknesses of the other layers and the nonmagnetic support may be determined by the same method as the thickness of the magnetic layer, or may be determined by a known film thickness measurement method. Or you may obtain | require as design thickness computed from manufacturing conditions, such as application | coating conditions. The thickness of the magnetic layer is more preferably in the range of 10 nm to 100 nm, and still more preferably in the range of 20 to 90 nm. There may be at least one magnetic layer, and the magnetic layer may be separated into two or more layers having different magnetic characteristics, and a configuration related to a known multilayer magnetic layer can be applied.
非磁性層の厚みは、０．０１〜０．６０μｍの範囲であることが好ましく、０．０５〜０．２０μｍの範囲であることがより好まく、０．１０〜０．２０μｍの範囲であることが更に好ましい。 The thickness of the nonmagnetic layer is preferably in the range of 0.01 to 0.60 μm, more preferably in the range of 0.05 to 0.20 μm, and in the range of 0.10 to 0.20 μm. More preferably.
バックコート層の厚みは、０．９０μｍ以下であることが好ましく、０．１０〜０．７０μｍの範囲であることが更に好ましい。 The thickness of the backcoat layer is preferably 0.90 μm or less, and more preferably in the range of 0.10 to 0.70 μm.
＜製造方法＞
（各層形成用組成物の調製）
磁性層、または任意に設けられる非磁性層、バックコート層を形成するための組成物は、先に説明した各種成分とともに、通常、溶媒を含む。溶媒としては、一般に塗布型磁気記録媒体製造のために使用される各種有機溶媒を挙げることができる。具体的には、任意の比率でアセトン、メチルエチルケトン、メチルイソブチルケトン、ジイソブチルケトン、シクロヘキサノン、イソホロン、テトラヒドロフラン、等のケトン類、メタノール、エタノール、プロパノール、ブタノール、イソブチルアルコール、イソプロピルアルコール、メチルシクロヘキサノールなどのアルコール類、酢酸メチル、酢酸ブチル、酢酸イソブチル、酢酸イソプロピル、乳酸エチル、酢酸グリコール等のエステル類、グリコールジメチルエーテル、グリコールモノエチルエーテル、ジオキサンなどのグリコールエーテル系、ベンゼン、トルエン、キシレン、クレゾール、クロルベンゼンなどの芳香族炭化水素類、メチレンクロライド、エチレンクロライド、四塩化炭素、クロロホルム、エチレンクロルヒドリン、ジクロルベンゼン等の塩素化炭化水素類、Ｎ，Ｎ−ジメチルホルムアミド、ヘキサン等を使用することができる。
<Manufacturing method>
(Preparation of each layer forming composition)
The composition for forming the magnetic layer or the optionally provided nonmagnetic layer and backcoat layer usually contains a solvent together with the various components described above. Examples of the solvent include various organic solvents generally used for producing a coating type magnetic recording medium. Specifically, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, etc., methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, methylcyclohexanol, etc. at an arbitrary ratio Alcohols, methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetates such as glycol acetate, glycol dimethyl ether, glycol monoethyl ether, dioxane and other glycol ethers, benzene, toluene, xylene, cresol, chlorobenzene Aromatic hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin Chlorinated hydrocarbons such as dichlorobenzene, N, N- dimethylformamide, may be used hexane.
磁性層、または任意に設けられる非磁性層、バックコート層を形成するための組成物を調製する工程は、通常、少なくとも混練工程、分散工程、およびこれらの工程の前後に必要に応じて設けた混合工程からなる。個々の工程はそれぞれ２段階以上に分かれていてもかまわない。本発明で用いられる強磁性粉末、結合剤、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下の非磁性粒子、各種添加剤、溶媒などすべての原料はどの工程の最初または途中で添加してもかまわない。また、個々の原料を２つ以上の工程で分割して添加してもかまわない。例えば、結合剤を混練工程、分散工程、分散後の粘度調整のための混合工程で分割して投入してもよい。上記磁気記録媒体の製造方法では、従来の公知の製造技術を一部の工程として用いることができる。混練工程ではオープンニーダ、連続ニーダ、加圧ニーダ、エクストルーダなど強い混練力をもつものを使用することが好ましい。これらの混練処理の詳細については特開平１−１０６３３８号公報、特開平１−７９２７４号公報に記載されている。また、各層形成用組成物を分散させるには、ガラスビーズやその他のビーズを用いることができる。このような分散ビーズとしては、高比重の分散ビーズであるジルコニアビーズ、チタニアビーズ、スチールビーズが好適である。これら分散ビーズは、粒径と充填率を最適化して用いることが好ましい。分散機は公知のものを使用することができる。 The step of preparing the magnetic layer, or the optionally provided nonmagnetic layer and the composition for forming the backcoat layer, is usually provided at least before and after the kneading step, the dispersing step, and these steps. It consists of a mixing process. Each process may be divided into two or more stages. Ferromagnetic powder, binder used in the present invention, all raw materials such as non-magnetic particles, various additives, solvents with a ratio of long axis length to short axis length (long axis length / short axis length) of 1.5 or less May be added at the beginning or during any step. In addition, individual raw materials may be added in two or more steps. For example, the binder may be divided and added in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion. In the method for manufacturing the magnetic recording medium, a conventional known manufacturing technique can be used as a part of the process. In the kneading step, it is preferable to use a kneading force such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-1-79274. Moreover, in order to disperse each layer forming composition, glass beads or other beads can be used. As such dispersed beads, zirconia beads, titania beads, and steel beads, which are dispersed beads having a high specific gravity, are suitable. These dispersed beads are preferably used by optimizing the particle size and filling rate. A well-known thing can be used for a disperser.
（塗布工程）
磁性層は、磁性層形成用組成物を非磁性層上に直接、または非磁性層形成用組成物と逐次もしくは同時に重層塗布することにより形成することができる。バックコート層は、バックコート層形成用組成物を、非磁性支持体の磁性層を有する（または磁性層が追って設けられる）側とは反対側に塗布することにより形成することができる。各層形成のための塗布の詳細については、特開２０１０−２３１８４３号公報段落００６６を参照できる。
(Coating process)
The magnetic layer can be formed by applying the magnetic layer forming composition directly on the nonmagnetic layer, or by sequentially or simultaneously with the nonmagnetic layer forming composition. The back coat layer can be formed by applying the composition for forming the back coat layer on the side opposite to the side having the magnetic layer of the nonmagnetic support (or the magnetic layer is provided later). JP, 2010-231843, A paragraph 0066 can be referred to for the details of application for formation of each layer.
（その他工程）
磁気記録媒体製造のためのその他の各種工程については、特開２０１０−２３１８４３号公報段落００６７〜００７０を参照できる。
(Other processes)
JP, 2010-231843, A paragraphs 0067-0070 can be referred to for other various processes for manufacture of a magnetic recording medium.
（好ましい製造方法の一態様）
好ましい製造方法としては、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下の非磁性粒子を、磁気記録媒体の磁性層側表面に局在させ得る製造方法である以下の製造方法を挙げることができる。
上記磁気記録媒体の製造方法であって、
磁性層形成工程を含み、
上記磁性層形成工程は、
強磁性粉末および結合剤を含む磁性塗布膜形成用組成物、ただし、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である非磁性粒子を含まない、を非磁性支持体上に、直接または一層以上の他の層（例えば上記非磁性層）を介して塗布および乾燥することにより磁性塗布膜を形成すること、
上記磁性塗布膜上に、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である複数個の非磁性粒子および溶媒を含むオーバーコート液を塗布および乾燥することにより上記非磁性粒子を上記磁性塗布膜上に配置すること、
上記配置した非磁性粒子を上記磁性塗布膜側へ押し込むことにより、強磁性粉末および結合剤を含み、かつ上記非磁性粒子が上記状態で存在する上記磁性層を形成すること、
を含む、上記磁気記録媒体の製造方法。
以下に、上記磁気記録媒体の製造方法について、更に詳細に説明する。
(One aspect of preferred production method)
As a preferred production method, production in which nonmagnetic particles having a major axis length / minor axis length ratio (major axis length / minor axis length) of 1.5 or less can be localized on the magnetic layer side surface of the magnetic recording medium. The following manufacturing methods which are methods can be mentioned.
A method for producing the magnetic recording medium, comprising:
Including a magnetic layer forming step,
The magnetic layer forming step includes
Composition for forming magnetic coating film containing ferromagnetic powder and binder, except for non-magnetic particles having a major axis length / minor axis length ratio (major axis length / minor axis length) of 1.5 or less Forming a magnetic coating film on the non-magnetic support directly or through one or more other layers (for example, the non-magnetic layer) and drying.
On the magnetic coating film, an overcoat liquid containing a plurality of nonmagnetic particles and a solvent having a major axis length / minor axis length ratio (major axis length / minor axis length) of 1.5 or less is applied and dried. By disposing the non-magnetic particles on the magnetic coating film,
Forming the magnetic layer containing ferromagnetic powder and a binder and having the nonmagnetic particles present in the state by pushing the arranged nonmagnetic particles toward the magnetic coating film;
A method for manufacturing the magnetic recording medium, comprising:
Hereinafter, the method for producing the magnetic recording medium will be described in more detail.
上記磁気記録媒体の製造方法は、磁性層形成工程において、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である非磁性粒子を含まない磁性塗布膜の形成〜上記非磁性粒子の押し込みまでの工程を行う点以外は、通常の塗布型磁気記録媒体の製造方法と同様に行うことができる。 In the magnetic layer forming step, the magnetic recording medium manufacturing method includes a magnetic coating film that does not contain non-magnetic particles having a ratio of a major axis length to a minor axis length (major axis length / minor axis length) of 1.5 or less. The method can be performed in the same manner as in the production method of an ordinary coating type magnetic recording medium except that the steps from the formation of the above to the pressing of the nonmagnetic particles are performed.
上記磁性塗布膜の形成は、この塗布膜を形成するための組成物として、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である非磁性粒子を含まない組成物を用いる点以外は、通常の磁性層の形成と同様に行うことができる。例えば、上記磁性塗布膜は、この塗布膜を形成するための組成物を非磁性支持体上に直接、または非磁性層形成用組成物と逐次もしくは同時に重層塗布することにより形成することができる。 The magnetic coating film is formed by using, as a composition for forming the coating film, nonmagnetic particles having a major axis length / minor axis length ratio (major axis length / minor axis length) of 1.5 or less. Except for using a composition that does not contain, it can be carried out in the same manner as the formation of a normal magnetic layer. For example, the magnetic coating film can be formed by coating the composition for forming the coating film directly on the nonmagnetic support, or sequentially or simultaneously with the nonmagnetic layer forming composition.
形成した磁性塗布膜上に塗布するオーバーコート液は、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下である複数個の非磁性粒子および溶媒を含む。溶媒としては、先に記載した各種有機溶媒を用いることができ、上記非磁性粒子がコロイド粒子の場合には、コロイド粒子が安定に分散し得る溶媒を用いることが好ましい。本発明および本明細書におけるコロイド粒子は、先に記載したように、少なくとも、メチルエチルケトン、シクロヘキサノン、トルエンもしくは酢酸エチル、または上記溶媒の二種以上を任意の混合比で含む混合溶媒の少なくとも１つの有機溶媒１００ｍＬあたり１ｇ添加した際に、沈降せず分散しコロイド分散体をもたらすことのできる粒子をいうため、上記溶媒から選択した溶媒を、コロイド粒子を含むオーバーコート液の調製に用いることは好ましい。オーバーコート液中の上記非磁性粒子の濃度は、例えば５〜５０質量％程度とすることができるが、この範囲に限定されるものではない。なおオーバーコート液には、上記非磁性粒子および溶媒に加えて、任意の量で潤滑剤が含まれていてもよい。 The overcoat liquid applied on the formed magnetic coating film contains a plurality of non-magnetic particles and a solvent having a ratio of major axis length to minor axis length (major axis length / minor axis length) of 1.5 or less. . As the solvent, the above-described various organic solvents can be used. When the nonmagnetic particles are colloidal particles, it is preferable to use a solvent in which the colloidal particles can be stably dispersed. As described above, the colloidal particles in the present invention and the present specification include at least one organic solvent in a mixed solvent containing at least methyl ethyl ketone, cyclohexanone, toluene or ethyl acetate, or two or more of the above-mentioned solvents in any mixing ratio. When 1 g per 100 mL of solvent is added, it refers to particles that can be dispersed without precipitation to yield a colloidal dispersion. Therefore, it is preferable to use a solvent selected from the above solvents for the preparation of an overcoat solution containing colloidal particles. The concentration of the nonmagnetic particles in the overcoat liquid can be, for example, about 5 to 50% by mass, but is not limited to this range. The overcoat liquid may contain a lubricant in an arbitrary amount in addition to the nonmagnetic particles and the solvent.
上記オーバーコート液の塗布および乾燥は、通常の磁性層形成用組成物の塗布および乾燥と同様に（または準じて）行うことができる。これにより、上記磁性塗布膜上に、上記非磁性粒子を配置することができる。 The application and drying of the overcoat liquid can be carried out in the same manner as (or in accordance with) the usual application and drying of the magnetic layer forming composition. Thereby, the nonmagnetic particles can be arranged on the magnetic coating film.
上記磁性塗布膜上に配置された上記非磁性粒子を、上記磁性塗布膜側へ押し込むことにより、強磁性粉末および結合剤を含み、かつ上記非磁性粉末が、比率ｂ／ｔの平均値が０．９以下の状態で存在する磁性層を形成することができる。上記非磁性粒子の押し込みは、カレンダ処理等の磁気記録媒体の表面平滑化処理として公知の方法により行うことができる。ここでの押し込みの程度を、カレンダ圧等によって制御することにより、比率ｂ／ｔの平均値を調整することができる。 By pushing the nonmagnetic particles arranged on the magnetic coating film into the magnetic coating film side, the nonmagnetic powder contains a ferromagnetic powder and a binder, and the nonmagnetic powder has an average ratio b / t of 0. A magnetic layer existing in a state of .9 or less can be formed. The indentation of the nonmagnetic particles can be performed by a known method as a surface smoothing process of a magnetic recording medium such as a calendar process. The average value of the ratio b / t can be adjusted by controlling the degree of pressing here by the calendar pressure or the like.
以上、好ましい製造方法の一態様を説明したが、本発明の一態様にかかる磁気記録媒体は、上記製造方法によって製造されたものに限定されるものではない。 As mentioned above, although the one aspect | mode of the preferable manufacturing method was demonstrated, the magnetic recording medium concerning one aspect | mode of this invention is not limited to what was manufactured by the said manufacturing method.
［磁気信号再生装置］
本発明の一態様は、上記磁気記録媒体と磁気再生ヘッドとを含む磁気信号再生装置に関する。
[Magnetic signal reproducing device]
One aspect of the present invention relates to a magnetic signal reproducing apparatus including the magnetic recording medium and a magnetic reproducing head.
上記磁気信号再生装置は、磁気記録媒体として、上記の本発明の一態様にかかる磁気記録媒体を有するものであれば、その他については公知技術を何ら制限なく適用することができる。 As long as the magnetic signal reproducing apparatus has the magnetic recording medium according to one embodiment of the present invention as the magnetic recording medium, other known techniques can be applied without any limitation.
好ましい一態様では、上記磁気信号再生装置において、上記磁気記録媒体に２５０ｋｆｃｉ以上の線記録密度で記録された磁気信号を、磁気再生ヘッドで再生することができる。本発明の磁気テープは、例えば２００ｋｆｃｉ以上、更には２５０ｋｆｃｉ以上の高線記録密度で磁気信号を記録し再生するために好適に用いることができる。なお線記録密度は、例えば８００ｋｆｃｉ以下であるが、８００ｋｆｃｉ超でもよい。 In a preferred aspect, in the magnetic signal reproducing apparatus, a magnetic signal recorded on the magnetic recording medium at a linear recording density of 250 kfci or more can be reproduced by a magnetic reproducing head. The magnetic tape of the present invention can be suitably used for recording and reproducing magnetic signals at a high linear recording density of, for example, 200 kfci or more, and further 250 kfci or more. The linear recording density is, for example, 800 kfci or less, but may be more than 800 kfci.
磁気信号の記録再生に関しては、磁気記録媒体の磁性層側表面に存在する突起は、記録再生時の磁気ヘッド／磁気記録媒体表面間のスペーシングを増大させる。この点に関し、スペーシング増大による出力低下Ｌｓは以下の関係にあることが知られている。以下において、ｄ＝磁気ヘッド／磁気記録媒体表面間のスペーシング［ｎｍ］、λ＝記録波長［ｎｍ］である。
Ｌｓ［ｄＢ］＝５４．６（ｄ／λ）
上記の関係からわかるように、記録波長が短くなる（短波長記録化する）ほどスペーシングを小さくすることで出力低下を抑制できる。短波長記録化は高密度記録化と同義であるため、記録密度を高めるほどスペーシングを小さくすることにより、出力低下を抑制することができる。この点に関し、本発明者は、高さ２０ｎｍ以上の突起が多く存在することは、高密度記録領域においてスペーシングによる出力低下を引き起こし得ると考えている。これに対し、高さ２０ｎｍ以下の突起の個数を先に記載した範囲に抑えるとともに、高さ５ｎｍ以上の突起を先に記載した個数存在させることにより、高密度記録領域においても、優れた電磁変換特性の達成と、走行時の摩擦係数の低減が、ともに可能になると、本発明者は推察している。
With respect to recording and reproduction of magnetic signals, the protrusions present on the magnetic layer side surface of the magnetic recording medium increase the spacing between the magnetic head and the magnetic recording medium surface during recording and reproduction. In this regard, it is known that the output decrease Ls due to the increase in spacing is in the following relationship. In the following, d = spacing between the magnetic head and the surface of the magnetic recording medium [nm], and λ = recording wavelength [nm].
Ls [dB] = 54.6 (d / λ)
As can be seen from the above relationship, a decrease in output can be suppressed by reducing the spacing as the recording wavelength becomes shorter (shorter wavelength recording). Since short wavelength recording is synonymous with high density recording, lowering the output can be suppressed by reducing the spacing as the recording density is increased. In this regard, the present inventor believes that the presence of many protrusions having a height of 20 nm or more can cause a decrease in output due to spacing in the high-density recording region. On the other hand, the number of protrusions having a height of 20 nm or less is limited to the above-described range, and the number of protrusions having a height of 5 nm or more is made to exist so that excellent electromagnetic conversion can be achieved even in a high-density recording region. The present inventor has inferred that it is possible to achieve both characteristics and to reduce the friction coefficient during traveling.
上記磁気信号再生装置の構成等の詳細については、特開２０１０−２３１８４３号公報段落００７２〜００７３も参照できる。 JP, 2010-231843, A paragraphs 0072-0073 can also be referred to for details, such as composition of the above-mentioned magnetic signal reproducing device.
以下に、本発明を実施例に基づき説明する。但し、本発明は実施例に示す態様に限定されるものではない。なお、以下に記載の「部」、「％」の表示は、特に断らない限り、「質量部」、「質量％」を示す。 Hereinafter, the present invention will be described based on examples. However, this invention is not limited to the aspect shown in the Example. In addition, unless otherwise indicated, the display of "part" described below and "%" shows "mass part" and "mass%".
以下に記載する実施例１〜５、７、比較例３で用いたシリカコロイド粒子（コロイダルシリカ）は、それぞれゾルゲル法により調製された市販のシリカコロイド粒子であり、前述の各種粉末の平均粒子サイズの測定方法により測定した平均粒子サイズ（平均長軸長）、標準偏差、粒子サイズの変動係数（ＣＶ値）および平均針状比は、以下の表１に示す値であった。これらシリカコロイド粒子は、先に記載したコロイド粒子の定義に当てはまる性質を有していた。
比較例１、４で用いたシリカコロイド粒子（コロイダルシリカ）は、それぞれ水ガラス法により調製された市販のシリカコロイド粒子であり、前述の各種粉末の平均粒子サイズの測定方法により測定した平均粒子サイズ（平均長軸長）、標準偏差、粒子サイズの変動係数（ＣＶ値）および平均針状比は、以下の表１に示す値であった。これらシリカコロイド粒子は、先に記載したコロイド粒子の定義に当てはまる性質を有していた。
実施例６、比較例５で用いた珪素酸化物粒子は、それぞれ先に記載したコロイド粒子の定義に当てはまらない市販の珪素酸化物粒子（粉末シリカ）であり、前述の各種粉末の平均粒子サイズの測定方法により測定した平均粒子サイズ（平均長軸長）、標準偏差、粒子サイズの変動係数（ＣＶ値）および平均針状比は、以下の表１に示す値であった。
比較例２で用いたカーボンブラックは、先に記載したコロイド粒子の定義に当てはまらない市販のカーボンブラックであり、前述の各種粉末の平均粒子サイズの測定方法により測定した平均粒子サイズ（平均長軸長）、標準偏差、粒子サイズの変動係数（ＣＶ値）および平均針状比は、以下の表１に示す値であった。
The silica colloidal particles (colloidal silica) used in Examples 1 to 5, 7 and Comparative Example 3 described below are commercially available silica colloidal particles prepared by the sol-gel method, and the average particle sizes of the various powders described above. The average particle size (average major axis length), standard deviation, particle size variation coefficient (CV value), and average needle ratio measured by the measurement methods were the values shown in Table 1 below. These silica colloidal particles had properties that met the definition of colloidal particles described above.
The silica colloidal particles (colloidal silica) used in Comparative Examples 1 and 4 are commercially available silica colloidal particles prepared by the water glass method, and the average particle size measured by the above-described method for measuring the average particle size of various powders. (Average major axis length), standard deviation, variation coefficient of particle size (CV value) and average needle ratio were values shown in Table 1 below. These silica colloidal particles had properties that met the definition of colloidal particles described above.
The silicon oxide particles used in Example 6 and Comparative Example 5 are commercially available silicon oxide particles (powder silica) that do not meet the definition of colloidal particles described above, and the average particle sizes of the various powders described above. The average particle size (average major axis length), standard deviation, particle size variation coefficient (CV value), and average needle ratio measured by the measurement method were the values shown in Table 1 below.
The carbon black used in Comparative Example 2 is a commercially available carbon black that does not meet the definition of colloidal particles described above, and the average particle size (average major axis length) measured by the above-described method for measuring the average particle size of various powders. ), Standard deviation, coefficient of variation in particle size (CV value) and average needle ratio were the values shown in Table 1 below.
［実施例１］
（１）磁性塗布膜形成用組成物の処方
（磁性液）
強磁性六方晶バリウムフェライト粉末：１００．０部
（保磁力Ｈｃ：１７５ｋＡ／ｍ（２２００Ｏｅ）、平均粒子サイズ（平均板径）：２０ｎｍ）
オレイン酸：２．０部
塩化ビニル共重合体（日本ゼオン製ＭＲ−１０４）：１０．０部
スルホン酸基含有ポリエステルポリウレタン樹脂（東洋紡製ＵＲ−４８００）：４．０部
メチルエチルケトン：１５０．０部
シクロヘキサノン：１５０．０部
（研磨剤液）
ダイヤモンド粒子（平均粒子サイズ：５０ｎｍ、平均針状比：４．０）：６．０部
スルホン酸基含有ポリエステルポリウレタン樹脂（東洋紡製ＵＲ−４８００）：０．６部
シクロヘキサノン：２３部
（潤滑剤・硬化剤溶液）
ステアリン酸：２．０部
ステアリン酸アミド：０．３部
ステアリン酸ブチル：６．０部
メチルエチルケトン：１１０．０部
シクロヘキサノン：１１０．０部
ポリイソシアネート（日本ポリウレタン製コロネートＬ）：３．０部
[Example 1]
(1) Formulation of magnetic coating film forming composition (magnetic liquid)
Ferromagnetic hexagonal barium ferrite powder: 100.0 parts (coercive force Hc: 175 kA / m (2200 Oe), average particle size (average plate diameter): 20 nm)
Oleic acid: 2.0 parts vinyl chloride copolymer (MR-104 manufactured by Nippon Zeon): 10.0 parts sulfonic acid group-containing polyester polyurethane resin (UR-4800 manufactured by Toyobo): 4.0 parts methyl ethyl ketone: 150.0 parts Cyclohexanone: 150.0 parts (abrasive solution)
Diamond particles (average particle size: 50 nm, average needle ratio: 4.0): 6.0 parts sulfonic acid group-containing polyester polyurethane resin (UR-4800 manufactured by Toyobo): 0.6 parts cyclohexanone: 23 parts (lubricant Hardener solution)
Stearic acid: 2.0 parts Stearic acid amide: 0.3 parts Butyl stearate: 6.0 parts Methyl ethyl ketone: 110.0 parts Cyclohexanone: 110.0 parts Polyisocyanate (Nihon Polyurethane Coronate L): 3.0 parts
（２）非磁性層形成用組成物の処方
ベンガラ（平均粒子サイズ：０．１５μｍ、平均針状比：７、ＢＥＴ（Brunauer-Emmett-Teller）比表面積：５２ｍ２／ｇ）：７５．０部
カーボンブラック（平均粒子サイズ：１６ｎｍ、ＤＢＰ（dibutyl phthalate）吸油量：７４ｃｍ３／１００ｇ）：２５．０部
フェニルホスホン酸：３．０部
塩化ビニル共重合体（日本ゼオン製ＭＲ−１０４）：１２．０部
スルホン酸基含有ポリエステルポリウレタン樹脂（東洋紡製ＵＲ−８４０１）：８．０部
メチルエチルケトン：３７０．０部
シクロヘキサノン：３７０．０部
ステアリン酸：１．０部
ステアリン酸アミド：０．３部
ステアリン酸ブチル：２．０部
ポリイソシアネート（日本ポリウレタン製コロネートＬ）：５．０部
(2) Prescription of composition for forming nonmagnetic layer Bengala (average particle size: 0.15 μm, average needle ratio: 7, BET (Brunauer-Emmett-Teller) specific surface area: 52 m 2 / g): 75.0 parts carbon black (average particle size: 16nm, DBP (dibutyl phthalate) oil absorption amount: 74cm 3 /100g):25.0 parts phenylphosphonic acid: 3.0 parts vinyl chloride copolymer (Nippon Zeon MR-104): 12 0.0 part sulfonic acid group-containing polyester polyurethane resin (UR-8401 manufactured by Toyobo Co., Ltd.): 8.0 parts methyl ethyl ketone: 370.0 parts cyclohexanone: 370.0 parts stearic acid: 1.0 part stearic acid amide: 0.3 part stearin Butyl acid: 2.0 parts Polyisocyanate (Japan Polyurethane Coronate L): 5.0 parts
（３）バックコート層形成用組成物の処方
カーボンブラック（平均粒子サイズ：４０ｎｍ、ＤＢＰ吸油量：７４ｃｍ３／１００ｇ）：１００．０部
銅フタロシアニン：３．０部
ニトロセルロース：２５．０部
スルホン酸基含有ポリエステルポリウレタン樹脂（東洋紡製ＵＲ−８４０１）：６０．０部
ポリエステル樹脂（東洋紡製バイロン５００）：４．０部
アルミナ粉末（ＢＥＴ比表面積１７ｍ２／ｇのα−アルミナ）：１．０部
ポリイソシアネート（日本ポリウレタン製コロネートＬ）：１５．０部
メチルエチルケトン：６００．０部
トルエン：６００．０部
(3) Formulation of carbon black of the back coat layer forming composition (average particle size: 40 nm, DBP oil absorption: 74cm 3 /100G):100.0 parts of copper phthalocyanine: 3.0 parts Nitrocellulose: 25.0 parts sulfone Acid group-containing polyester polyurethane resin (UR-8401 manufactured by Toyobo): 60.0 parts polyester resin (Byron 500 manufactured by Toyobo): 4.0 parts alumina powder (α-alumina having a BET specific surface area of 17 m 2 / g): 1.0 Parts Polyisocyanate (Japan Polyurethane Coronate L): 15.0 parts Methyl ethyl ketone: 600.0 parts Toluene: 600.0 parts
（４）各層形成用組成物の調製
磁性塗布膜形成用組成物は、以下の方法によって調製した。
上記磁性液をオープンニーダにより混練・希釈処理後、横型ビーズミル分散機により、ビーズ径０．１ｍｍのジルコニア（ＺｒＯ２）ビーズ（以下、「Ｚｒビーズ」と記載する）を用い、ビーズ充填率８０体積％、ローター先端周速１０ｍ／秒で、１パス滞留時間を２分とし、３０パスの分散処理を行った。
研磨剤液は、上記成分を、ビーズ径０．３ｍｍのＺｒビーズとともに、横型ビーズミル分散機に、［ビーズ体積／（研磨剤液体積＋ビーズ体積）］×１００が８０％になるように調整して入れ、１２０分間ビーズミル分散処理を行い、処理後の液を取り出し、フロー式の超音波分散ろ過装置を用いて、超音波分散ろ過処理を施した。
磁性液、研磨剤液、および上記潤滑剤・硬化剤溶液をディゾルバー攪拌機に導入し、周速１０ｍ／秒で３０分間攪拌した後、フロー式超音波分散機により流量７．５ｋｇ／分で３パス処理した後に、１μｍの平均孔径を有するフィルタでろ過して磁性塗布膜形成用組成物を調製した。
非磁性層形成用塗布液は以下の方法によって作製した。
潤滑剤（ステアリン酸、ステアリン酸アミド、ステアリン酸ブチル）およびポリイソシアネートを除く、上記成分をオープンニーダにより混練・希釈処理して、その後、横型ビーズミル分散機により分散処理を実施した。その後、潤滑剤およびポリイソシアネートを添加して、ディゾルバー攪拌機にて攪拌・混合処理を施して非磁性層形成用組成物を調製した。
バックコート層形成用組成物は、以下の方法によって調製した。
ポリイソシアネートを除く、上記成分をディゾルバー攪拌機に導入し、周速１０ｍ／秒で３０分間攪拌した後、横型ビーズミル分散機により分散処理を実施した。その後、ポリイソシアネートを添加して、ディゾルバー攪拌機にて攪拌・混合処理を施し、バックコート層形成用組成物を調製した。
(4) Preparation of composition for forming each layer The composition for forming a magnetic coating film was prepared by the following method.
After kneading and diluting the magnetic liquid with an open kneader, using a zirconia (ZrO 2 ) bead having a bead diameter of 0.1 mm (hereinafter referred to as “Zr beads”) with a horizontal bead mill disperser, a bead filling rate of 80 volumes %, The rotor tip peripheral speed was 10 m / sec, the residence time for one pass was 2 minutes, and 30 pass dispersion treatment was performed.
For the abrasive liquid, adjust the above components together with Zr beads with a bead diameter of 0.3 mm to a horizontal bead mill disperser so that [bead volume / (abrasive liquid volume + bead volume)] × 100 is 80%. Then, a bead mill dispersion treatment was performed for 120 minutes, the treated liquid was taken out, and an ultrasonic dispersion filtration treatment was performed using a flow type ultrasonic dispersion filtration apparatus.
The magnetic liquid, abrasive liquid, and the above lubricant / curing agent solution are introduced into a dissolver stirrer, stirred for 30 minutes at a peripheral speed of 10 m / sec, and then 3 passes at a flow rate of 7.5 kg / min with a flow ultrasonic disperser. After the treatment, it was filtered through a filter having an average pore size of 1 μm to prepare a composition for forming a magnetic coating film.
The nonmagnetic layer forming coating solution was prepared by the following method.
The above components except for the lubricant (stearic acid, stearic acid amide, butyl stearate) and polyisocyanate were kneaded and diluted with an open kneader, and then dispersed with a horizontal bead mill disperser. Thereafter, a lubricant and polyisocyanate were added, and the mixture was stirred and mixed with a dissolver stirrer to prepare a composition for forming a nonmagnetic layer.
The composition for forming a backcoat layer was prepared by the following method.
The above components excluding polyisocyanate were introduced into a dissolver stirrer and stirred for 30 minutes at a peripheral speed of 10 m / second, and then subjected to dispersion treatment with a horizontal bead mill disperser. Thereafter, polyisocyanate was added, and the mixture was stirred and mixed with a dissolver stirrer to prepare a composition for forming a backcoat layer.
（５）磁気テープの作製
（非磁性層、バックコート層および磁性塗布膜の形成）
厚さ６．００μｍのポリエチレンナフタレート支持体上に、乾燥後の厚さが０．１０μｍになるように非磁性層形成用組成物を塗布し乾燥させた後、バックコート層形成用組成物を、上記支持体の非磁性層を形成した面とは反対側の面に、乾燥後の厚さが０．５０μｍになるように塗布し乾燥させた。こうして非磁性層とバックコート層を形成した支持体を一度巻き取り、雰囲気温度７０℃の環境で３６時間熱処理を行った。熱処理後、非磁性層上に、上記磁性塗布膜形成用組成物を塗布し乾燥させ、磁性塗布膜を形成した。
その後、金属ロールのみから構成されるカレンダロールで速度４０ｍ／ｍｉｎ、線圧３００ｋｇ／ｃｍ（２９４ｋＮ／ｍ）、カレンダロールの表面温度１００℃で表面平滑化処理（カレンダ処理）を行った。
(5) Production of magnetic tape (formation of nonmagnetic layer, backcoat layer and magnetic coating film)
A composition for forming a nonmagnetic layer was applied on a polyethylene naphthalate support having a thickness of 6.00 μm so that the thickness after drying was 0.10 μm and dried, and then the composition for forming a backcoat layer was formed. The surface of the support opposite to the surface on which the nonmagnetic layer was formed was applied and dried so that the thickness after drying was 0.50 μm. The support on which the nonmagnetic layer and the backcoat layer were thus formed was wound up once and subjected to a heat treatment for 36 hours in an environment with an atmospheric temperature of 70 ° C. After the heat treatment, the magnetic coating film forming composition was applied onto the nonmagnetic layer and dried to form a magnetic coating film.
Thereafter, a surface smoothing treatment (calendar treatment) was performed at a speed of 40 m / min, a linear pressure of 300 kg / cm (294 kN / m), and a calender roll surface temperature of 100 ° C. with a calender roll composed of only a metal roll.
（オーバーコート液の調製）
シリカコロイド粒子（コロイダルシリカＡ）２０．０部を、メチルエチルケトン８０．０部中に分散させてオーバーコート液を調製した。
(Preparation of overcoat solution)
An overcoat solution was prepared by dispersing 20.0 parts of silica colloidal particles (colloidal silica A) in 80.0 parts of methyl ethyl ketone.
（磁性層の形成）
調製したオーバーコート液を、上記磁性塗布膜上に、磁性塗布膜に含まれる強磁性六方晶バリウムフェライト粉末１００．０部に対するシリカコロイド粒子の量が以下の表２に記載の量となるように塗布量を調整して塗布、乾燥させることで、上記磁性塗布膜上にシリカコロイド粒子を配置した。
その後金属ロールのみから構成されるカレンダロールで速度４０ｍ／ｍｉｎ、線圧３００ｋｇ／ｃｍ（２９４ｋＮ／ｍ）、カレンダロールの表面温度１００℃でカレンダ処理を行い、上記磁性塗布膜上に配置したシリカコロイド粒子を磁性塗布膜側に押し込み磁性層を形成した、
その後、雰囲気温度７０℃の環境で３６時間熱処理を行った。熱処理後、１／２インチ（０．０１２７メートル）幅にスリットを行った。スリット後、サファイア製ブレードと不織布が磁性層表面に押し当たるように取り付けたテープクリーニング装置で磁性層表面のクリーニングを行い、磁気記録媒体（磁気テープ）を得た。
(Formation of magnetic layer)
In the prepared overcoat solution, the amount of colloidal silica particles relative to 100.0 parts of the ferromagnetic hexagonal barium ferrite powder contained in the magnetic coating film on the magnetic coating film is set to the amount shown in Table 2 below. The colloidal silica particles were arranged on the magnetic coating film by adjusting the coating amount and applying and drying.
Thereafter, the silica colloid disposed on the magnetic coating film was calendered with a calender roll composed of only a metal roll at a speed of 40 m / min, a linear pressure of 300 kg / cm (294 kN / m), and a calender roll surface temperature of 100 ° C. The magnetic layer was formed by pushing the particles to the magnetic coating film side.
Thereafter, heat treatment was performed for 36 hours in an environment with an atmospheric temperature of 70 ° C. After the heat treatment, slits were made to a width of 1/2 inch (0.0127 meter). After slitting, the surface of the magnetic layer was cleaned with a tape cleaning device attached so that the sapphire blade and the nonwoven fabric pressed against the surface of the magnetic layer to obtain a magnetic recording medium (magnetic tape).
［実施例２〜７、比較例２、５］
オーバーコート液に、表１に示す非磁性粒子を、磁性塗布膜に含まれる強磁性六方晶バリウムフェライト粉末１００．０部に対する各非磁性粒子の量が、以下の表２に記載の量になるように塗布量を調整して塗布、乾燥させた点以外、実施例１と同様の方法で磁気記録媒体（磁気テープ）を得た。実施例７については、形成する磁性塗布膜を厚くするために、実施例１より磁性塗布膜形成用組成物の塗布量を増量した。
[Examples 2 to 7, Comparative Examples 2 and 5]
In the overcoat solution, the amount of each nonmagnetic particle shown in Table 1 with respect to 100.0 parts of the ferromagnetic hexagonal barium ferrite powder contained in the magnetic coating film is the amount shown in Table 2 below. Thus, a magnetic recording medium (magnetic tape) was obtained in the same manner as in Example 1 except that the coating amount was adjusted and coating and drying were performed. In Example 7, the coating amount of the composition for forming a magnetic coating film was increased from that in Example 1 in order to thicken the magnetic coating film to be formed.
［比較例１、３、４］
磁性液に、表１に示す非磁性粒子を、磁性液に含まれる強磁性六方晶バリウムフェライト粉末１００．０部に対する各非磁性粒子の量が、以下の表２に記載の量になるように添加した点、およびオーバーコート液の塗布からカレンダ処理までの工程を実施しなかった点以外、実施例１と同様の方法で磁気記録媒体（磁気テープ）を得た。
[Comparative Examples 1, 3, 4]
In the magnetic liquid, the amount of each nonmagnetic particle shown in Table 1 with respect to 100.0 parts of the ferromagnetic hexagonal barium ferrite powder contained in the magnetic liquid is the amount shown in Table 2 below. A magnetic recording medium (magnetic tape) was obtained in the same manner as in Example 1 except that the steps from the addition of the overcoat liquid to the calendering were not performed.
［評価方法］
１．比率ｂ／ｔの平均値
実施例、比較例の磁気テープについて、先に記載した方法によりＳＥＭ像を撮像し、先に記載した方法により磁性層厚みｔを求めた。更に、撮像したＳＥＭ像において、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下のすべての非磁性粒子を特定し、先に記載した方法により、比率ｂ／ｔを求めた。
比較例２、比較例５では、長軸長と短軸長との比率（長軸長／短軸長）が１．５以下の非磁性粒子は確認されなかったため、代わりに、比較例２については撮像したＳＥＭ像において特定したカーボンブラック、比較例５については撮像したＳＥＭ像において特定した珪素酸化物粒子について、先に記載した方法により、比率ｂ／ｔを求めた。
上記実施例、比較例では、上記特定した非磁性粒子とともに磁性層に含まれている非磁性粒子であるダイヤモンド粒子は、平均針状比が上記の通り４．０であり、上記特定した非磁性粒子とは形状が大きく異なる。したがって、ＳＥＭ像において、ダイヤモンド粒子と上記特定した非磁性粒子とは、容易に区別することができた。ただし前述の組成分析可能な公知の方法により、各種粒子を特定することも可能である。
実施例、比較例の磁気テープについて、先に記載した方法により磁性層におけるダイヤモンド粒子の比率（長軸長／短軸長）を求めたところ、磁性層に含まれるすべてのダイヤモンド粒子の比率（長軸長／短軸長）は、１．５を大きく超え、４．０程度であった。
なお断面観察用試料の作製は、以下に記載の方法により行った。
（ｉ）磁気テープの幅方向１０ｍｍ×厚み方向１０ｍｍのサイズの試料を剃刀を用いて切り出した。
切り出した試料の磁性層表面に保護膜を形成して保護膜付試料を得た。保護膜の形成は、以下の方法により行った。
上記試料の磁性層表面に、スパッタリングにより白金（Ｐｔ）膜（厚み３０ｎｍ）を形成した。白金膜のスパッタリングは、下記条件で行った。
＜白金膜のスパッタリング条件＞
ターゲット：Ｐｔ
スパッタリング装置のチャンバー内真空度：７Ｐａ以下
電流値：１５ｍＡ
上記で作製した白金膜付試料に、更に厚み１００〜１５０ｎｍのカーボン膜を形成した。カーボン膜の形成は、下記（ｉｉ）で用いるＦＩＢ（集束イオンビーム）装置に備えられた、ガリウムイオン（Ｇａ＋）ビームを用いるＣＶＤ（Chemical vapor deposition）機構により行った。
（ｉｉ）上記（ｉ）で作製した保護膜付試料に対し、ＦＩＢ装置によりガリウムイオン（Ｇａ＋）ビームを用いるＦＩＢ加工を行い磁気テープの断面を露出させた。ＦＩＢ加工における加速電圧は３０ｋＶ、プローブ電流は１３００ｐＡとした。
こうして露出させた断面観察用試料を、上記比率ｂ／ｔの平均値を求めるためのＳＥＭ観察に用いた。
[Evaluation method]
1. Average value of ratio b / t About the magnetic tape of an Example and a comparative example, the SEM image was imaged by the method described previously, and magnetic layer thickness t was calculated | required by the method described previously. Further, in the captured SEM image, all non-magnetic particles having a ratio of major axis length to minor axis length (major axis length / minor axis length) of 1.5 or less are specified, and the ratio is determined by the method described above. b / t was determined.
In Comparative Example 2 and Comparative Example 5, since non-magnetic particles having a ratio of the major axis length to the minor axis length (major axis length / minor axis length) of 1.5 or less were not confirmed, instead of Comparative Example 2 For carbon black identified in the imaged SEM image, and for Comparative Example 5, the ratio b / t was determined for the silicon oxide particles identified in the imaged SEM image by the method described above.
In the examples and comparative examples, diamond particles, which are nonmagnetic particles contained in the magnetic layer together with the specified nonmagnetic particles, have an average needle ratio of 4.0 as described above, and the specified nonmagnetic The shape is very different from the particles. Therefore, in the SEM image, the diamond particles and the specified nonmagnetic particles could be easily distinguished. However, it is also possible to specify various particles by a known method capable of analyzing the composition.
For the magnetic tapes of Examples and Comparative Examples, when the ratio of diamond particles (major axis length / minor axis length) in the magnetic layer was determined by the method described above, the ratio of all diamond particles contained in the magnetic layer (long axis) (Axis length / minor axis length) greatly exceeded 1.5 and was about 4.0.
The cross-sectional observation sample was produced by the method described below.
(I) A sample having a size of 10 mm in the width direction and 10 mm in the thickness direction of the magnetic tape was cut out using a razor.
A protective film was formed on the surface of the magnetic layer of the cut sample to obtain a sample with a protective film. The protective film was formed by the following method.
A platinum (Pt) film (thickness 30 nm) was formed on the surface of the magnetic layer of the sample by sputtering. Sputtering of the platinum film was performed under the following conditions.
<Sputtering conditions for platinum film>
Target: Pt
Vacuum degree in chamber of sputtering apparatus: 7 Pa or less Current value: 15 mA
A carbon film having a thickness of 100 to 150 nm was further formed on the platinum film-prepared sample prepared above. The carbon film was formed by a CVD (Chemical Vapor Deposition) mechanism using a gallium ion (Ga + ) beam provided in an FIB (focused ion beam) apparatus used in (ii) below.
(Ii) The sample with the protective film prepared in the above (i) was subjected to FIB processing using a gallium ion (Ga + ) beam by an FIB apparatus to expose the cross section of the magnetic tape. The acceleration voltage in FIB processing was 30 kV, and the probe current was 1300 pA.
The thus-exposed sample for cross-sectional observation was used for SEM observation for obtaining the average value of the ratio b / t.
２．平均長軸長φ、φ／ｔ
実施例１〜７、比較例１、３、４については、上記１．で特定した長軸長と短軸長との比率（長軸長／短軸長）が１．５以下の非磁性粒子の長軸長の算術平均（平均長軸長）φを算出し、上記１．で求めた磁性層の厚みｔとの比率φ／ｔを求めた。
比較例２については、上記１．で特定したカーボンブラック、比較例５については上記１．で特定した珪素酸化物粒子の長軸長の算術平均（平均長軸長）φを算出し、上記１．で求めた磁性層の厚みｔとの比率φ／ｔを求めた。
また、ここで求めた平均長軸長φおよび長軸長の標準偏差σから変動係数（ＣＶ値）を算出したところ、実施例、比較例で用いた各非磁性粒子について、表１に示すＣＶ値と同じ値であった。
2. Average long axis length φ, φ / t
About Examples 1-7 and Comparative Examples 1, 3, and 4, the above 1. The arithmetic average (average major axis length) φ of the major axis length of the nonmagnetic particles having a ratio of major axis length to minor axis length (major axis length / minor axis length) specified in (1) of 1.5 or less is calculated, and 1. The ratio φ / t with respect to the thickness t of the magnetic layer obtained in step 1 was obtained.
For Comparative Example 2, the above 1. For the carbon black specified in 1 and Comparative Example 5, 1. 1. Calculate the arithmetic average (average major axis length) φ of the major axis length of the silicon oxide particles specified in 1 above. The ratio φ / t with respect to the thickness t of the magnetic layer obtained in step 1 was obtained.
Further, when the coefficient of variation (CV value) was calculated from the average major axis length φ and the standard deviation σ of the major axis length obtained here, the non-magnetic particles used in Examples and Comparative Examples are shown in Table 1. The value was the same as the value.
３．磁気テープの磁性層側表面においてＡＦＭにより測定される突起の個数
実施例、比較例の磁気テープについて、先に記載した方法により、高さ５ｎｍ以上の突起の個数、および高さ２０ｎｍ以上の突起の個数を求めた。
3. Number of protrusions measured by AFM on the magnetic layer side surface of the magnetic tape For the magnetic tapes of Examples and Comparative Examples, the number of protrusions having a height of 5 nm or more and protrusions having a height of 20 nm or more were measured by the method described above. The number was determined.
４．電磁変換特性の評価
実施例、比較例の各磁気テープについて、ＳＮＲを、磁気ヘッドを固定した１／２インチ（０．０１２７メートル）リールテスターで測定した。磁気ヘッド／磁気テープ相対速度は５．５ｍ／ｓｅｃとした。記録はＭＩＧ（Metal-In-Gap）ヘッド（ギャップ長０．１５μｍ、トラック幅１．０μｍ）を使い、記録電流は各磁気テープの最適記録電流に設定した。再生ヘッドには素子厚み１５ｎｍ、シールド間隔０．１μｍ、リード幅０．５μｍのＧＭＲ（Giant-Magnetoresistive）ヘッドを用いた。線記録密度（５４０ｋｆｃｉ）の信号を記録し、再生信号をシバソク社製のスペクトラムアナライザーで測定し、キャリア信号の出力と、スペクトル全帯域の積分ノイズとの比をＳＮＲとした。得られたＳＮＲを、以下の基準で電磁変換特性を評価した。評価結果がＡであれば、電磁変換特性のより一層の向上が達成されたと判断することができる。
比較例１のＳＮＲを０．０ｄＢとし、
ＳＮＲ ＋０．５ｄＢ超：Ａ
ＳＮＲ −０．５ｄＢ以上＋０．５ｄＢ以下：Ｂ
ＳＮＲ −０．５ｄＢ未満：Ｃ
4). Evaluation of Electromagnetic Conversion Characteristics For each of the magnetic tapes of Examples and Comparative Examples, SNR was measured with a 1/2 inch (0.0127 meter) reel tester to which a magnetic head was fixed. The relative speed of the magnetic head / magnetic tape was 5.5 m / sec. For recording, a MIG (Metal-In-Gap) head (gap length 0.15 μm, track width 1.0 μm) was used, and the recording current was set to the optimum recording current of each magnetic tape. A GMR (Giant-Magnetoresistive) head having an element thickness of 15 nm, a shield interval of 0.1 μm, and a lead width of 0.5 μm was used as the reproducing head. A signal having a linear recording density (540 kfci) was recorded, and the reproduced signal was measured with a spectrum analyzer manufactured by Shiba-Soku Co., Ltd., and the ratio of the carrier signal output to the integrated noise in the entire spectrum band was defined as SNR. The obtained SNR was evaluated for electromagnetic conversion characteristics according to the following criteria. If the evaluation result is A, it can be determined that a further improvement in electromagnetic conversion characteristics has been achieved.
The SNR of Comparative Example 1 is 0.0 dB,
SNR + more than 0.5dB: A
SNR −0.5 dB or more +0.5 dB or less: B
SNR less than -0.5 dB: C
５．摩擦係数の測定
ＡＦＭで４０μｍ角（４０μｍ×４０μｍ）で測定した時の中心線平均表面粗さＲａが１５ｎｍで直径が４ｍｍのＡｌＴｉＣ（アルミナチタンカーバイド）製の丸棒に、実施例、比較例の各磁気テープを、磁気テープの幅方向が丸棒の軸方向と平行になるように丸棒に巻き付けて、磁気テープの一方の端に１００ｇの重りを吊り下げ他方の端をロードセルに取り付けた状態で、１４ｍｍ／ｓｅｃの速度で磁気テープを１パスあたり４５ｍｍ摺動させ、合計１００パス摺動を繰り返した。この時の１パス目、１００パス目の等速で摺動中の荷重をロードセルで検出して測定値を得て、以下の式：
摩擦係数＝ｌｎ（測定値（ｇ）／１００（ｇ））／π
に基づいて摩擦係数を算出した。１パス目および１００パス目の摩擦係数両方を、下記基準で評価した。
０．３０未満：Ａ
０．３０以上０．４０未満：Ｂ
０．４０以上０．５０未満：Ｃ
０．５０以上またはハリツキが発生し測定できず：Ｄ
評価結果がＡまたはＢであれば、走行時の摩擦係数の低減が達成されたと判断することができる。
5. Measurement of coefficient of friction When measured with an AFM at a 40 μm square (40 μm × 40 μm), the center line average surface roughness Ra is 15 nm and the diameter is 4 mm. A round bar made of AlTiC (alumina titanium carbide) is used in Examples and Comparative Examples. Each magnetic tape is wound around a round bar so that the width direction of the magnetic tape is parallel to the axial direction of the round bar, a weight of 100 g is suspended at one end of the magnetic tape, and the other end is attached to the load cell Then, the magnetic tape was slid by 45 mm per pass at a speed of 14 mm / sec, and a total of 100 passes were repeated. At this time, the load during sliding at the constant speed of the first pass and the 100th pass is detected by a load cell to obtain a measured value, and the following formula:
Friction coefficient = ln (measured value (g) / 100 (g)) / π
The coefficient of friction was calculated based on Both the first pass and the 100th pass coefficient of friction were evaluated according to the following criteria.
Less than 0.30: A
0.30 or more and less than 0.40: B
0.40 or more and less than 0.50: C
0.50 or more or cracking occurs and cannot be measured: D
If the evaluation result is A or B, it can be determined that the reduction of the friction coefficient during traveling has been achieved.
以上の結果を、表２に示す。 The results are shown in Table 2.
表２に示す結果から、実施例の磁気テープは、走行時の摩擦係数が低く、かつ優れた電磁変換特性を発揮したことが確認できる。 From the results shown in Table 2, it can be confirmed that the magnetic tape of the example exhibited a low coefficient of friction during running and exhibited excellent electromagnetic conversion characteristics.
本発明は、バックアップテープ等の高密度記録用磁気記録媒体の技術分野において有用である。 The present invention is useful in the technical field of magnetic recording media for high density recording such as backup tapes.
Claims (14)
前記磁性層は、長軸長と短軸長との比率、長軸長／短軸長、が１．５以下である複数個の非磁性粒子を含み、
前記複数個の非磁性粒子は、走査型電子顕微鏡により撮像される断面画像において観察される各非磁性粒子の磁性層埋没深さをｂ、磁性層の厚みをｔとして、比率ｂ／ｔの平均値が０．９以下の状態で前記磁性層に存在し、
前記磁気記録媒体の磁性層側の表面において原子間力顕微鏡により測定される突起の個数は、面積４０μｍ×４０μｍあたり、高さ５ｎｍ以上の突起の個数が８００個以上であり、かつ高さ２０ｎｍ以上の突起の個数が２０個以下である磁気記録媒体。 A magnetic recording medium having a magnetic layer comprising a ferromagnetic powder and a binder on a nonmagnetic support,
The magnetic layer includes a plurality of nonmagnetic particles having a ratio of a major axis length to a minor axis length, a major axis length / minor axis length of 1.5 or less,
The plurality of nonmagnetic particles have an average ratio b / t, where b is the buried depth of the magnetic layer of each nonmagnetic particle observed in a cross-sectional image taken by a scanning electron microscope, and t is the thickness of the magnetic layer. Present in the magnetic layer with a value of 0.9 or less,
The number of protrusions measured by an atomic force microscope on the surface of the magnetic recording medium on the magnetic recording medium is 800 or more protrusions having a height of 5 nm or more per area of 40 μm × 40 μm, and a height of 20 nm or more. A magnetic recording medium having 20 protrusions or less.
磁気再生ヘッドと、
を含む磁気信号再生装置。 The magnetic recording medium according to any one of claims 1 to 11,
A magnetic reproducing head;
A magnetic signal reproducing apparatus.
磁性層形成工程を含み、
前記磁性層形成工程は、
強磁性粉末および結合剤を含む磁性塗布膜形成用組成物、ただし、長軸長と短軸長との比率、長軸長／短軸長、が１．５以下である非磁性粒子を含まない、を非磁性支持体上に、直接または一層以上の他の層を介して塗布および乾燥することにより磁性塗布膜を形成すること、
前記磁性塗布膜上に、長軸長と短軸長との比率、長軸長／短軸長、が１．５以下である複数個の非磁性粒子および溶媒を含むオーバーコート液を塗布および乾燥することにより前記非磁性粒子を前記磁性塗布膜上に配置すること、
前記配置した非磁性粒子を前記磁性塗布膜側へ押し込むことにより、強磁性粉末および結合剤を含み、かつ前記非磁性粒子が前記状態で存在する前記磁性層を形成すること、
を含む、前記磁気記録媒体の製造方法。 A method of manufacturing a magnetic recording medium according to any one of claims 1 to 11,
Including a magnetic layer forming step,
The magnetic layer forming step includes
Composition for forming magnetic coating film containing ferromagnetic powder and binder, except for non-magnetic particles having a ratio of major axis length to minor axis length, major axis length / minor axis length of 1.5 or less Forming a magnetic coating film on the non-magnetic support directly or through one or more other layers and drying.
On the magnetic coating film, an overcoat liquid containing a plurality of nonmagnetic particles and a solvent having a ratio of major axis length to minor axis length, major axis length / minor axis length of 1.5 or less, and drying is applied and dried. By disposing the non-magnetic particles on the magnetic coating film,
Forming the magnetic layer containing the ferromagnetic powder and the binder and having the nonmagnetic particles present in the state by pushing the arranged nonmagnetic particles toward the magnetic coating film;
A method for manufacturing the magnetic recording medium, comprising:
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| JP6058607B2 (en) | 2014-09-30 | 2017-01-11 | 富士フイルム株式会社 | Magnetic tape and manufacturing method thereof |
| JP6334490B2 (en) * | 2015-09-30 | 2018-05-30 | 富士フイルム株式会社 | Magnetic recording medium, magnetic signal reproducing apparatus, and method of manufacturing magnetic recording medium |
| JP6684255B2 (en) | 2017-09-07 | 2020-04-22 | 富士フイルム株式会社 | Magnetic recording medium and magnetic recording / reproducing apparatus |
| JP7377164B2 (en) | 2020-05-08 | 2023-11-09 | 富士フイルム株式会社 | Magnetic recording media, magnetic tape cartridges, and magnetic recording and reproducing devices |
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| US11410696B2 (en) | 2020-01-24 | 2022-08-09 | Fujifilm Corporation | Magnetic recording medium, magnetic recording and reproducing apparatus, magnetic tape cartridge, and magnetic tape cartridge group |
| US11482250B2 (en) | 2020-01-24 | 2022-10-25 | Fujifilm Corporation | Magnetic recording medium, magnetic recording and reproducing apparatus, magnetic tape cartridge, and magnetic tape cartridge group |
| US11538494B2 (en) | 2020-01-24 | 2022-12-27 | Fujifilm Corporation | Magnetic recording and reproducing device |
| JP7377164B2 (en) | 2020-05-08 | 2023-11-09 | 富士フイルム株式会社 | Magnetic recording media, magnetic tape cartridges, and magnetic recording and reproducing devices |
| WO2022209316A1 (en) * | 2021-03-31 | 2022-10-06 | ソニーグループ株式会社 | Magnetic recording medium |
Also Published As
| Publication number | Publication date |
|---|---|
| US20210174829A1 (en) | 2021-06-10 |
| JP6334490B2 (en) | 2018-05-30 |
| US10229708B2 (en) | 2019-03-12 |
| US11514942B2 (en) | 2022-11-29 |
| US10957352B2 (en) | 2021-03-23 |
| US20170092314A1 (en) | 2017-03-30 |
| US20190156859A1 (en) | 2019-05-23 |
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